Looks likea WW1 dog tag...but I see no name or number on it. Size,metal type and pic of back may help, but at this time it may just be a blank unengraved disc.
Yep, they had lots of uses! Since I don't believe they were mentioned, they were also used as tags for Telephone/Electric Poles and sometimes on meters for Gas, Electric and possibly Water.
AnyAny underground mines near you? Miners are assigned a numbered tag. When they enter the mine the tag gets hung on a board by the entrance. It is how they keep track of who is in and who is out. We have the one from wife's grandfather. Very similar. Called miner check tag.