At first sight I like your buckle, but I would very much like to know what is stamped on the backside in the lower part of the diamond. I think I can se a RZM-sign and some numbers - could you take a real close-up pic of it ?? so we can see if it match the RZM-label.
Michael
Looks like M5/276 to me which would make it a Klein & Quenzer. This company is known to have marked its buckles with the incorrect M code (should be M4 obviously). The placement of the MM inside the diamond is also an oddity with K&Q buckles.
Looking at the pics again I can see what Gerry sees (even though I see it as M3 in stead of M5, but the pic is i.m.o. not clear enough to see if it is 3 or 5) and as M4/115 (as stamped on the RZM-label) is Klein & Quenzer all fit in