The 5th Mass. Artillery (Battery E) served as a member of McGilvery’s Brigade in the Artillery Reserve, Army of the Potomac. The unit was commanded by Captain Charles A. Phillips (1841-1876), a law student from Boston & a recent graduate of Harvard University. He became Major of U.S. volunteers by brevet, and was discharged from the service at the close of the war in July, 1865. From what I read, this man was truly charmed or incredibly lucky to not only escape death but also injury when on a consistent basis when everything around him was being destroyed. His unit's job was to actual expose themselves to the enemy to cover important movements of other portions of the army. His garments were often pierced with bullets. Horses were shot from under him. On another occasion he took a wounded comrade on his horse, to carry him to the rear when a cannon ball killed both the wounded man & the horse without harm to him. Under his command, 104 men were engaged at Gettysburg and among them 2 were killed and 14 were wounded.
In his post-war life, he continued his profession & practiced law in Nevada. I had to do some digging to figure out when exactly he died. On Tuesday, April 4, 1876 the first report of his death was announced in the Salem Gazette which then wrote an obituary for him on April 18, 1876 in anticipation of his funeral in the family lot in Harmony Grove. The initial news of his death was reported on Friday April 4, but the newspaper account states indirectly he died on March 20, 1876. It took 11 days for the news to reach the east.
The 5th Mass. Battery tablet is located on the left or west side of South Hancock Ave. if traveling north & is surrounded by two 3-inch ordnance rifles. If facing the monument, the gun on the left is no. 612, the one on the right is a War Dept. reproduction. The PA State Monument looms large and is due north not too far away. 
Parking is available at small, cutout shoulders along the road. Be sure to stay off the grass or you will be ticketed by park police. I visited this monument on Thursday, July 5, 2012 in the later part of the afternoon & was at an elevation of 575 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
These cast iron monuments were first built in 1900 and concluded in 1906 according to the NRHP nomination form. All of this tablet nonsense is very confusing and disorganized. I will go with 1901 for this tablet, using the the NRHP's date of 1900 as a guide. At any rate, it is amazing with all the work and effort exerted to make the Gettysburg National Military Park a reality, no one took the time to keep accurate records & correct installation dates. The work was done under the direction of the Gettysburg National Park Commission (established by the U.S. Department of War), after they took over the administration of the park from the Gettysburg Battlefield Memorial Association (whose funds had expired) on March 3, 1893, and whose stewardship was then transferred to the National Park Service in 1933. SOURCE
Draw the Sword, using descriptive help from the NPS site, offers the following description: Iron War Department tablet. Painted inscription tablet, 3’8"x3'. Mounted on a fluted post, 4’4" high. Tablet cast by Calvin Gilbert, founder.
These battery tablets were cast by Calvin Gilbert. Gilbert joined the 87th Pennsylvania Volunteers when the "Rebellion" broke out. Since he was musically inclined, he was made a member of the regimental band. In early 1863, he was promoted to the rank of Captain and sent to Washington D.C. for commissary duty. He served in that capacity until the war ended in 1865, and at war’s end earned the brevet rank of Major. 
After returning home to Gettysburg, Major Gilbert moved his family to the town of Chambersburg, where he served as the Superintendent of Schools. He also opened an iron foundry there in 1868. When Calvin learned, nearly thirty years later, in 1894, that the Gettysburg Foundry was available, he purchased it with a business partner and moved his family back to Gettysburg. For the next twenty years, the Calvin Gilbert Foundry created ironworks that are still seen today on many historic forts and national battlefields (this tablet), from upstate New York to Florida to Lookout Mountain. Gilbert lived to be 100 years old and attended the Last Reunion of the Blue and Gray for the 75th anniversary of the Battle of Gettysburg when he was 99. He was a most remarkable man and lived an amazing life.
Look carefully on the reverse side of one of these tablets and his name might be there; I found a tablet or two like this. The inscription on the monument reads:
Army of the Potomac
First Brigade Artillery Reserve
Massachusetts Light Artillery
5th Battery E
Six 3 inch Rifles
Captain Charles A. Phillips Commanding
July 2 Withdrew at 5 p.m. from the field near the Peach Orchard and went into Battery here.
July 3 About 1.30 p.m. by order of Brig. General H.J. Hunt fired on the Confederate Batteries but did little damage. Opened an enfilading fire soon after on Longstreet's advancing line of Infantry and assisted in repulsing the assault. A charge was made within the range of the Battery immediately afterwards by the Florida Brigade and at about the same time a Confederate Battery opened on the left front which at once received the concentrated fire of the Batteries of the Brigade driving the cannoneers from their guns which they abandoned.
July 4 Remained in this position until afternoon.
Casualties. Killed 2 men. Wounded 1 officer and 13 men. Total 16.
There are hundreds of non-sculpted monumentation for the various Confederate States & Union units which fought at Gettysburg. There are about 10 different variations of tablets, markers and monoliths by my reckoning. Six designs represent brigade (2), division (2), corps (2), & army headquarters (2), each different in a subtle way so as to distinguish between armies. Battalion/battery/advance position markers and regimental monuments for United States Regulars & Confederate have their own distinct design (2), bringing the total to ten designs at the battlefield. The bronze tablets (the brigade monuments) were created by Albert Russell & Sons Co. of Newburyport, Massachusetts. The granite bases which accompany the various tablets were created by the Van Amringe Company out of Boston, Massachusetts. The cast iron tablets were of course manufactured by the aforementioned Calvin Gilbert. The 1910 Gettysburg Commission report lists the awarded contracts to these companies (not Gilbert) for the tablets. All of these tablets were designed by architect Colonel Emmor Bradley Cope (July 23, 1834 - May 28, 1927). He designed pretty much every tablet for both the Union and Confederate armies, each one distinct, with several different varieties. He is buried in Evergreen Cemetery 
in Gettysburg, as well he should be as this park and most of the things seen here today were designed by him and as such, are his legacy. These monuments/tablets were erected just after the turn of the century during the first and beginning of the second decade of the 20th century. Each one has since been preserved or restored at least twice since the turn of the 21st century. The plaques and tablets were erected by the Gettysburg Park Commission (established by the War Department). The Gettysburg Park Commission is also referred to as the Gettysburg National Military Park Commission or the Gettysburg National Park Commission, to clear up any confusions, especially my own.
On October 1, 1898, the Gettysburg National Park Commission in a letter to the Secretary of War gave recommendations for continuing the task of organizing and progressing the work of the Gettysburg National Military Park. Every November they wrote their annual report which outlined the work of the GNPC for that year. The following is an excerpt from that report relevant to this waymark. The link at the end of the paragraph will take you to the entire report. The method of marking the positions of troops on this field, as approved by the War Department, is to place the principal tablet or monument of each command at the position occupied by the command in the main line of battle, and to mark the several important positions subsequently reached by each command in the course of the battle by subordinate and ancillary tablets, with appropriate brief inscriptions giving interesting details and occurrences and noting the day and hour as nearly as possible. SOURCE
Most of the Commission reports have been digitized and can be found HERE. The initial 1893 report up to and including 1921 can be found here. 1922 to 1926 are missing and have yet to be discovered. The years 1927 to 1933 were discovered in 1996 and are also included. To my knowledge this is the most comprehensive list of documents that illustrated the development and formation of the park.
Information about these specific types of monuments:
UNION & CONFEDERATE BATTERY TABLETS (ADVANCED POSITION MARKERS)
These tablets are 3 feet 8 inches x 3 feet 4 inches in dimensions (although this one seems to be about 2 feet 6 inches on the short side), with carefully prepared inscriptions cast in raised letters painted in white (contrasting the black background) describing the part taken in the battle by each artillery battery, their position and stating its numbers & losses so far as practicable to obtain. The union tablets have iron tabs connected to the top denoting the Army of the Potomac and the order of battle. Most of the CS battery markers state the losses were not reported in detail. The brigade which each battery served under is written first on the tablet, then proceeded by the battery name, usually accompanied by some colorful artillery name. They are mounted on iron pillars or fluted cast iron posts about 3 feet high, grouted in the ground, and the tablets are inclined at a suitable angle so that the inscriptions can easily be read by persons riding or driving on the avenue. Every tablet is 4 feet 4 inches in height. The advance position markers were cast by Calvin Gilbert. SOURCE & SOURCE. These tablets usually have accompanying artillery pieces which flank the tablet on either side. There can be as little as one cannon and as many as four. The cannons usually represent the battery and the armaments that specific battery used at Gettysburg. The cannons presumably point in the same direction as they once fired at the enemy in 1863. Sometimes only the cannon pads are present as the guns are periodically removed for service, cleaning, restoration, maintenance, etc.
The 5th Massachusetts Battery tablet is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is cataloged as contributing structure no. MN553-B.
From the Nomination Form:
1 of 100 Civil War tablets in the park locating the positions of batteries and brigades not otherwise marked by monumentation. Marks position of Wilcox's CS Brigade Advance on July 2, 1863. Narrates events associated w/ Brigade during Battle..
Short Physical Description:
Tablet & 2 cannon. Painted inscription tablet, 3'8"x3'. Mounted on a fluted post, 4'4" high. Cannon located to left & right of tablet. Tablet cast by Calvin Gilbert, founder.
Long Physical Description:
N/A
My Sources
1.
NRHP Nomination Form
2.
Stone Sentinels
3.
Virtual Gettysburg
4.
Draw the Sword