That image on the front looks like a Spanish fort lookout tower to me (facing head on.) Maybe a souvenir buckle from Florida or some other Caribbean fort location? It does appear to be pretty old. Happy Hunting, Sub
The shape looks somewhat like a bell, but the "shoulders" are too angular, so I went with the fort theory! May be too small for military use, but you could research Puerto Rican home guard or Spanish military buckles. Sub