[itsybitsycoder]

That's probably not the tattoo that's meant. When most cats get neutered/first shots, they get a tattoo in the ear with a unique serial number, which includes a vet to contact. That way if the cat gets lost it can be tracked down. It was the only "permanent" way of doing it before microchips.

http://www.icam-coalition.org/downloads/Identification%20met...