There are a several dozen of these old, cast iron markers, most constructed and erected in 1896. E.B. Cope designed all of these markers as well as the tablets and historical markers, also made of cast iron. They were al completed under the direction of the War Department. The avenue, house and site markers are low to the ground, roadside and help to identify the various road systems, farmhouses, physical structures and historic sites like this one which play an important role in the historic district. Each marker is painted black with white letters.
These 61 cast iron tablets identify the names of the commemorative avenues in the park. Raised letters and the raised border of the tablet are painted a contrasting color to the black of the painted tablet. Each tablet is mounted on a fluted post and set at the terminus of the avenues. Designed by E. B. Cope. (NRHP narrative)
The tablet is planted roadside in the grass. The marker is located south or just before the intersection of United States Avenue. Beyond United States Avenue, Sedgwick becomes Hancock Avenue which leads to the Pennsylvania Memorial. There is a walking path a few feet to the north. The driveway for the George Weikert house is to the left. The Tompkins Brigade Tablet (MN526) is to the right or south of this by a few feet. Parking is available roadside and intermittently enlarges shoulder cutouts. Be sure to park on asphalt and not on grass. Park on anything green and you will be ticketed by park police. I visited the ID tablet on Thursday, July 5, 2012 @ 5:11 PM, EDT & @ an altitude of 542 feet, ASL. I used a Canon PowerShot 14.1 Megapixel, SX210 IS digital camera for the photos.
All the roads, avenue markers, house markers and the wide variety of Union & Confederate tablets seen around the battlefield and lining these avenues were designed by this architect, Colonel Emmor Bradley Cope (July 23, 1834 - May 28, 1927). 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.
This is a weird road. Sedgwick Avenue runs one way north as a continuation of Sykes Avenue from its intersection with Wheatfield Road. At the intersection with United States Avenue it continues as Hancock Avenue. The avenue was constructed by the War Department and links United States Avenue to the base of Little Round Top, intersecting Wheatfield Rd. Part of Sedwick's 6th Corps occupied ridge east of Avenue. The road follows the route first laid out in 1882 by Gettsyburg Battlefield Memorial Association.
The namesake of the marker, General John Sedgwick (September 13, 1813 - May 9, 1864), was a teacher, a career military officer, and a Union general in the American Civil War, and killed by a sniper's bullet at the Battle of Spotsylvania Court House. Sedwick was born in the Litchfield Hills town of Cornwall, Connecticut. He attended the U.S. Military Academy, and graduated in 1837.
The Sedgwick Avenue - Cast Iron Avenue 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. This roadside marker is a contributing structure but was accidentally omitted form the inventory and thus has no Identification number.
From the Nomination Form:
Part of post-Civil War cast-iron avenue tablets development of battlefield which now contributes to the commemorative landscape. Constructed by the War Department to mark United States Avenue.
Short Physical Description:
2, Painted raised letters and border inscription tablets, 2'9"x1'8". Mounted on fluted post, 3' high.
Long Physical Description:
N/A
My Sources
1.
NRHP Narrative
2.
Stone Sentinels
3.
Wikipedia