Were they found around an area that mined coal, if so that be my guess of what they are. I worked in a mine and the terms, its time to brass in or time to brass out was something you would hear someone say. Ours weren't that fancy looking and the mine would have a set of numbered stamp dies to number an employee's individual brass tag number. They were hung on a thing called a brass board. There were two tags for each employee. If one tag was hanging on the hook that meant the miner was underground and two of the same numbered tag on the hook said the miner was out of the mine. The tags are given to the employee and handed back to by the shift boss, who couldn't leave until all the hooks had two tags hanging on the board meaning everybody is on the surface.