found this elsewhere on T'net: It looks like yours but in rougher shape....
http://www.treasurenet.com/treasures/askmarkparker/201004.htm
TWELFTH KNIGHT
This shield-shaped pin is black at the top, with a red dragon holding a sword. The lower half is blue, with two crosses and a teepee in white. What is it, exactly?
It's the distinctive insignia, or DI, of the U.S. Army 12th Infantry Regiment. The upper portion, now darkened, was originally gold in color. Officially approved on June 20, 1923, the design incorporates a curious combination of symbols: the crosses, representing the iron fastenings of millstones, are said to recall the 12th's crushing losses (almost 50%) in the Civil War; the wigwam, Indian Wars service; red & gold- the colors of Spain- the Spanish-American War; the battlement, the capture of El Caney in that war; and the red sea-lion, from the arms of the Philippine Islands, the Philippine-American War. In Fine or better condition, with pin intact, it would be worth $15-25; as is, tarnished and fading, maybe half as much.