Marijuana belt buckle

I have a belt buckle and I'm not sure if it is brass or bronze it has no magnetism whatsoever. I beliee it from maybe the 60s or 70s. The number 851 is inscribed on the back. Which makes me believe not many of them were sold it says "851" But I have no direction on finding out information as I am from a small town with no decent pawn shops with educated people. Any information would greatly appreciated or direction on how to gain mor info. Thank you