The tag I'm thinking of was metallic as well. I'm sure it must have had a serial number stamped on it along with an address, but what I remember was that it was

The tag I'm thinking of was metallic as well. I'm sure it must have had a serial number stamped on it along with an address, but what I remember was that it was an irregular shape, perhaps with little flathead screwdriver-heads on the corners or something like that. And I'm not sure how accurate my memory from that time can possibly be, I imagine I only remember it because I was fascinated by the thought of putting something not-mail in the mailbox and I asked my father about it.