Hello,
You most likely have a somewhat one of a kind bracelet made in the late '60's thru '70's when 'hippies' now know as artisans were making jewelry like this. The TZA mark is not in any database that I could find. It was made by one of those 'Home Engraving' tools, that were purchased by folks back then and there are some still for sale now, for marking valuable items with their DL number in case it was ever stolen.
I would list it as vintage - you're really not sure what vintage and if it actually tests silver and the Onyx is real then your great. I would say it is a copy of a Native American type bracelet, I went on the database of Native American artisans and this mark was not among them although I did find a few that were signed with one of these types of engravers.
You certainly don't want to advertise it as Native, even though many did sand cast work. My experience and I admit it maybe limited, was that most Native sand cast work was better polished on the inside. My thought is that this artisan wanted to make sure folks knew it was sand cast and so left it somewhat rough on the inside.
I hope that this tiny amount of info helps.
Shar
