it may be....
Hey bud I was doing some research and saw something that looks just like it. Its looks like it could be part of, or something similar to a buckle that holds a sword, the site I saw it on was a spanish soldiers site.
Sword Belt Buckle, Ca. 1800-1820
Missing one of its two identical oval belt retaining elements, this Spanish regular issue cast brass serpentine "S"-hooked buckle shares similarities with other European sword belt buckles of the Napoleonic period. Some of these, captured from or left behind by Spanish forces, were worn by Mexican military units as late as the Mexican-American War (1846-1848).
http://www.artifacts.org/Bucklepage.htm the pic is near the bottom of the page. good luck J.D.