The Artillery Reserve was commanded by Brigadier General Robert Ogden Tyler (December 31, 1831 – December 1, 1874) was an American soldier who served as a general in the Union Army during the American Civil War. He is most known as the commander of the Artillery Reserve of the Army of the Potomac, including at the Battle of Gettysburg in July 1863 where many of his batteries played important role in the Union victory. Tyler later led a division of heavy artillery turned infantry during the Overland Campaign of 1864, when he was badly wounded and relegated to administrative duties for the duration of the war.
The Tyler’s Artillery Reserve - US Division Tablet, also known as the Army of The Potomac, Artillery Reserve, is located on Taneytown Road/Local Route 134 on the left or west side of the road if traveling north, at the Pleasonton Avenue intersection (which only turns west or left). The monument faces the east. The maintenance/facilities building is to the left or west of the monument on which property it stands. 
Parking is available on Pleasonton Avenue, on the side of the road. Don't park on Taneytown Road. Be sure to keep vehicles off the grass or you will be ticketed by park police. I visited this monument on Tuesday, August 7, 2012, Late in the afternoon. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
Draw the Sword, with descriptive help from the NPS site, offers the following description: Monuments are rough-hewn monoliths, 4 feet 2 inches x 2 feet x 7 feet in height, consisting of Winnsboro, South Carolina granite. Bronze inscription tablet, 3 feet 8 inches x 3 feet 6¾ inches, is affixed to the polished face of the monolith. One of 22 Union division monuments that describe the movements and itinerary of each division of the Army of the Potomac. Designed by E. B. Cope. There is supposed to be a bronze artillery corps insignia above tablet, but it is missing. The inscription on this tablet reads:
Army of the Potomac
Artillery Reserve
Brigadier General Robert O. Tyler
Captain James M. Robertson
Headquarter Guard
Thirty Second Massachusetts Infantry Co. C. Captain Josiah C. Fuller
First Regular Brigade Captain Dunbar R. Ransom
Four Batteries
First Volunteer Brigade Lieutenant Colonel Freeman McGilvery
Four Batteries
Second Volunteer Brigade Captain Elijah D. Taft
Four Batteries
Third Volunteer Brigade Captain James F. Huntington
Four Batteries
Fourth Volunteer Brigade Captain Robert H. Fitzhugh
Five Batteries
Train Guard
Fourth New Jersey (Seven Companies) Major Charles Ewing
Casualties: Killed 2 officers, 41 men; Wounded 15 officers, 172 men;
Captured or missing 12 men; Total 242.
There are hundreds of non-sculpted monumentation for the various Regular Union (Army of the Potomac - Federals) units & "Regular" Confederate units engaged at Gettysburg from July 1-3, 1863. There are about 10 different variations of tablets, markers & monoliths by my reckoning. Six designs represent brigade (2), division (2), corps (2), & army headquarters (only 2), each different in a subtle way so as to distinguish between armies. Battalion/battery/advance position markers & regimental monuments for U.S. Regulars & Confederate have their own distinct design (2), bringing the total to 10 designs at the battlefield. The bronze tablets (these ones, too) were created by Albert Russell & Sons Co. of Newburyport, Mass. The granite bases which accompany the various tablets were created by the Van Amringe Company from Boston, Mass. The cast iron tablets were manufactured by 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 & Rebel armies, each one distinct, w/ 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 were erected just after the turn of the century during the first & 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 & tablets were erected by the Gettysburg Park Commission (established by the War Dept.), 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 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 set gave recommendations for continuing the task of organizing & 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 & including 1921 can be found here. 1922 to 1926 are missing & 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:
DIVISION HEADQUARTERS MARKERS (For Union & Confederate Monuments)
Division headquarters are rectangular bronze tablets mounted on large, rectangular stones. Union headquarters have a corps or service branch symbol (like a cross, clover, star or crescent moon) as a separate bronze piece above the tablet (this one has the trefoil), while Confederate headquarters are labeled "C.S.A." on a separate bronze piece in an oval. There are 22 Union and 10 Confederate Division markers at Gettysburg. Both markers are of similar design and were all construed of Winnsboro (S.C.), granite. Each stands seven feet in height. SOURCE & SOURCE
The Tyler’s Artillery Reserve - US Division Tablet is a contributing feature to the Gettysburg Nat'l Military Park H.D. which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Gov't, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The monument is designated as structure no. MN447-A.
From the Nomination Form:
1 of 23 Civil War US Division Markers in Park. Records movements & itinerary of 2nd Corps, 2nd Division commanded by Brig. General John Gibbon.
Short Physical Description:
Monument w/ 1 cannon. Rough-hewn monolith, 4'2"x2'x7'H. Bronze inscription tablet, 3'8"x3'6-3/4", mounted on polished face. Bronze artillery corps insignia above tablet.
Long Physical Description:
Located west side of Taneytown Road at Pleasonton Avenue.
My Sources
1. NRHP Nomination Form
2. Stone Sentinels
3. Virtual Gettysburg
4. Draw the Sword
5. Historical Marker Database
6. Wikipedia