When I found this I thought I had another Buffalo Nickel, when I turned it over no Buffalo. I think it's a button. Just wondering when they were popular?
Not a button, but a "concho" I've seen these as decoration on belts, leather vests, motorcycle saddle bags... You can still order them online, but I don't know when they first appeared. If I had to guess I'd think maybe late 1960's at the oldest? I've seen some made from real nickles, but most seem to just be cast items...