Old Iron Luggage Tag???

[quicksilver]

I found what looks like a luggage tag from the early 1900's outside of a ballfield. The width is 1" and about 2" long and 1/8" thick. The metal appears to be entirely iron and the edges are "crimped" like the edge of a pastry or pasty. The lower back portion contains an engraved "U S A" with a couple of indiscernable numbers or letters above that. Could you please tell me what item I have here, the approx. age, value and history of the object. Thank you.

Matt

Wisconsin