We used to install similar tags many, many years ago at my uncle's radiator shop. They were made out of copper and soldered to a flat area on the upper tank. Any time a radiator came in for an overhaul, a tag was applied. It simply had an abbreviation for the name of the shop and a job number. If one ever needed to research what had been done to the radiator, you could simply call the shop and give the number to find out what had been done and when.
I've seen similar tags from other shops on old radiators. Some have dates, some don't.
My uncle's shop has been out of business for over forty years, so the tag wouldn't be much good other than for novelty purposes.
Matt
