This monument is considered a position marker for this regiment, secondary to the primary 17th Maine Infantry Monument. There are two types of Civil War position markers, those that are larger and significant enough to have their own NRHP listing and SIRIS listing and this type, which are considered insignificant and have neither. It is surprising this did not get recognition as it is an elaborate monument as far as these thing go.
The 17th Maine Infantry served as a member of De Trobriand’s Brigade in Birney’s Division of the Third Corps, Army of the Potomac, a Fighting 300 Regiment. The regiment was commanded by Lieutenant Colonel Benjamin Merrill (1827-1891), a graduate of Havard Law School (1849) and a lawyer in Portland either before and/or after the war. Under Merrill's command, the 17th Maine brought 292 men to the Gettysburg Battlefield and among them, 18 were killed, 112 were wounded and 3 went missing.
The position marker is located on the west or left side of 
Hancock Avenue if traveling north, just past the Pennsylvania State Monument, located on the west or left side of the road, northwest of the Pennsylvania Monument. The 9th Michigan Battery Monument is just to the left of this marker. The Pleasanton Avenue intersection is just north of this position. The front inscription faces the east, so you would be facing the west to read it. This location is a hot-bed of activity and one of the best examples of a hands-on history lesson of the Civil War one could hope to find. All along both sides of the road are these types of tablets, memorials, monuments, sculptures, and all manner of cannons, rifles and guns. Parking is available at enlarged shoulder cutouts on the right side of the road, directly across from the various monuments. Be sure to keep vehicles off the grass or you will be ticketed by park police. I visited this monument on Thursday, July 5, 2012 just before 6:00 P.M. I was at an elevation of 575 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
The monument can be described as a diamond-shaped sculpture with a square bottom standing on a low, rough-hewn base. The edges of the sculpture are also rough-hewn. There is a pink diamond with a polished surface set into the front face of the monument. The sculpture marks the July 3 position of the regiment in support of the 9th Michigan Artillery. The NRHP has the dimensions listed as: base: 4 feet 6 inches x 3 feet 2 inches; height: 6 feet. The front of the granite monument (faces the east) has an incised inscription under the red diamond (at the bottom) which reads:
Position of 17th Maine Infty. July 3, 1863.
Losing here killed 2. Wounded 10.
This regt. fought July 2 in the Wheatfield
as shown by monument there losing 120.
The 17th Maine Infantry Position Marker, monument and flank markers are all contributing features 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. Collectively, they are identified as structure number MN150-C.
From the Nomination Form:
Marks position held by 17th Maine Infantry during afternoon of July 2, 1863. 1 of 15 mns in Park to Maine troops at Gettysburg. Monument located on the south end of Wheatfield on DeTrobriand Avenue. The July 3, 1863, position marker is located on the west side Hancock Avenue, northwest of the Pennsylvania Monument.
Short Physical Description:
Mn, 2 flank markers, 1 position marker. Base, 8'x8'x2'3". Granite shaft 4'3" sq. w/ alternating smooth & rough courses topped w/ sculpted infantryman behing stone wall. Shaft Inscriptions & bronze inscrpt. tablet. Flank markers, slant faced, 1'6"x1'x2'. Position marker, base 4'6"x3'2", 6' h.
Long Physical Description:
Monument that has two flanking markers and one position marker. Monument is a 4.3 foot square granite shaft with alternating smooth and rough courses topped with a sculptured infantryman behind a stone wall and set on a 8.8x2.3 foot base. The shaft has inscriptions and a bronze inscription tablet. The flanking markers have slanted faces and are 1.6x1 foot. The position marker is six foot high on a 4.6x3.2 foot base. Monument is located at the south end of the Wheatfield on DeTrobriand Avenue. The position marker is located on the east side of Hancock Avenue.
Sources:
1.
NRHP Nomination Form
2.
SIRIS
3.
Stone Sentinels
4.
Virtual Gettysburg
5.
Draw the Sword
6.
Historical Marker Database