A gold metal and enamel device 1 5/32 inches (2.94cm) in height overall consisting of a shield blazoned: Azure, a bend Or. Attached below the shield a blue motto scroll inscribed "I SERVE" in gold letters.
The shield is blue for Infantry, with the bend taken from the coat of arms of Alsace.
The distinctive unit insignia was originally approved for the 51st Regiment Infantry on 24 Jan 1930; amended on 11 May 1937; redesignated for the 51st Infantry (Armored) on 23 Sep 1941; redesignated for the 51st Armored Infantry Regiment on 23 Apr 1942; redesignated for the 51st Armored Infantry Battalion on 6 Nov 1943; redesignated for the 51st Constabulary Squadron on 4 Dec 1946; redesignated for the 51st Armored Infantry Battalion on 22 Jun 1954 and redesignated for the 51st Infantry on 28 Jan 1958.