The monument to the 6th Maine Volunteers is south of Gettysburg on Howe Avenue. (39.783435° N, 77.228407° W; Google map; Tour map: Howe & Wright Avenues) It was dedicated in 1889 by the State of Maine.

Monument to the 6th Maine Infantry at Gettysburg

The 6th Maine was commanded at the Battle of Gettysburg by Colonel Hiram Burnham. It brought 439 men to the field and suffered no casualties, being held in reserve with Howe’s brigade in the rear of Big Round Top along Taneytown Road.

6th Corps Headquarters Flag 6C-1D

From the front of the monument:

6th Maine Infantry
3rd Brigde 1st Div. 6th Corps

From the side of the monument:

Held this position July 3, 1863.
In afternoon moved to support of centre, then to Big Round Top.

 See more on the 6th Maine Volunteer Infantry Regiment in the Civil War