As a child growing up on a farm, I remember lead tags like these were wired on rolls of fencing wire we got from Southern States. I guess they were lot number tags, but I am not sure.
Looks similar to phone company tags used to mark phone cables. Some were round and others square with a tab that went around the cable and back through a slot. These were mostly used in the buildings vaults(where the cables went into conduits) or in utility man holes to identify which cable it was.
However it most likely would be marked with a single number usually 1-35 or so and not such a high number so the mystery continues.