The 3rd Corps, 1st Division, 3rd Brigade was also known as De Trobriand’s Brigade. During the battle of Gettysburg, it served as a member of Birney’s Division in the Third Corps, Army of the Potomac. The brigade was commanded by Brevet Major General Philippe Régis Denis de Keredern de Trobriand (June 4, 1816 – July 15, 1897), a French aristocrat, lawyer, poet, and novelist who emigrated at a young age to the United States. De Trobriand was born at Chateau des Rochettes, near Tours, France. De Trobriand's military career is best known for the Battle of Gettysburg, where he first saw significant action. He arrived on the second day of battle, July 2, 1863, and took up positions in the area known as the Wheatfield. His brigade put up a spirited defense against powerful assaults by Confederate Maj. Gen. John Bell Hood's division, particularly a Georgia brigade under Brig. Gen. George T. Anderson and a South Carolina brigade under Brig. Gen. Joseph B. Kershaw. They were able to successfully hold out until relieved by units of Maj. Gen. John C. Caldwell's division of the II Corps, but it came at a terrible price—every third man in Trobriand's brigade was a casualty.
The DeTrobriand's Brigade - US Brigade Tablet is located on the left or siuthwest side of the road if traveling northwest along Sickles Avenue, just after the left turn for De Trobriand Avenue. 
Parking is available along intermittently widened shoulders which can accommodate a few vehicles at a time. I visited this site on Monday, July 1, 2013 on the 150th anniversary of the Battle of Gettysburg @ 5:40 PM, EDT & @ an altitude of 509 feet, ASL. As always, I used my trusty and oft abused Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
The monument work was done under the direction of the Gettysburg National Park Commission (established by the United States 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. According to the NRHP narrative, this monument was built in 1911 but finished in 1912, which according to my experience is questionable. I can't resolve if the 1912 date represents a completion of the physical construction of the tablet or an installation date. Other sources have it at 1910 & 1912. Another source wrote the last of the Confederate Brigade tablets was completed in December 1910. I don't know if anyone actually kept exact records of when these things were installed.
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 & 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.
There is an excellent excerpt in the American Guide Series about Gilbert attending the 75th reunion anniversary.
Look carefully on the reverse side on a few of these tablets and his name might be there; I found a tablet or two like this. This one of course is devoid of his name. The inscription on the monument reads:
Army of the Potomac
Third Corps First Division
Third Brigade
Col. P. Regis De Trobriand
17th. Maine 3d. 5th. Michigan 40th. New York
110th. (6 Cos.) Pennsylvania Infantry
July 2 Arrived at 10 a.m. On the advance of the Division between 2 and 3 p.m. the Brigade took position in column between First and Second Brigades for support to either. The 3d Michigan was sent to support First Brigade. The 17th Maine moved across the Wheatfield to the stone wall on the south. The 40th New York was sent to the gorge between the Devils's Den and Little Round Top. The 5th Michigan and 110th Penna. held the summit commanding a ravine in front and east of the Rose buildings until relieved by two Brigades of Fifth Corps when they retired through the Wheatfield where being joined by 17th Maine they held back a superior Confederate force until the arrival of First Division Second Corps when ammunition being exhausted this portion of the Brigade retired and at night was joined by the other regiments.
July 3 In Reserve.
Casualties. Killed 4 officers 71 men. Wounded 28 officers 366 men. Captured or missing 21 men. Total 490.
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 set 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:
BRIGADE HEADQUARTERS MARKERS (FOR UNION & CONFEDERATE TABLETS)
The Brigade Headquarters (and Confederate artillery battalions, equivalent to Union artillery brigades) are bronze tablets mounted at an angle on a stone pedestal and describe the movements and itinerary of each memorialized unit. Union headquarters have rounded tops and square bases. Confederate headquarters have flat tops and round bases. Union headquarters are marked with their corps or service branch symbol (like a diamond, cross, clover or crescent moon), while Confederate headquarters are simply labeled "C.S.A.". There are seventy-four brigade markers at Gettysburg honoring the Union's various brigades. (Other sources say there are seventy-five). There are sixty-four brigade markers honoring the Army of North Virginia's various brigades. The Union Brigade tablets consist of sea-green granite with a square 36” x 36” base; they weigh 3500 pounds. On each pedestal is mounted a bronze tablet with rounded corners weighing 300 pounds. They were built by Albert Russell & Sons Co. of Newburyport, Massachusetts and Charles Kappes. The Confederate Brigade tablets consist of red circular Maine granite bases 34 1/2 inches diameter and weighing 3,000 pounds. On each base is mounted a 300 pound bronze tablet. They were built by Van Amringe Granite Company (pedestals), Albert Russell & Sons Co., Newburyport, Mass (tablets) and Charles Kappes (foundations). SOURCE & SOURCE
The DeTrobriand's Brigade - US Brigade 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. MN482.
From the Nomination Form:
Short Physical Description:
Bronze inscription tablet, 4”0’ x 3’8”, attached to slant face of polished sea green granite monolith. 3’0” squared base of monument tapers to a smaller dimension at the tablet. All 5’4” H.
Long Physical Description:
Located N of DeTrobriand Ave at the Wheatfield, on Sickles Avenue.
Source
1. NRHP Nomination Form
2. Stone Sentinels
3. Virtual Gettysburg
4. Draw the Sword
5. Historical Marker Database
6. Wikipedia