Tattooing: Although tattoing ink is permanent, the cat's hair will in time grow over the area, making the ink virtually invisible to the naked eye. Only someone that shaves the cat in the proper spot will know how to find this number out. The number is kept on file at a feline registry.

In Europe it is required for any cat being sold to also be tattoed. The United States is a bit more lax. Tattooing is up to the owner. The places of choice to tattoo a cat is the inner thigh or inside the ear flap. Tattooing must be done by a qualified veterinarian or specialist, NOT at a the local tattoo parlor.

The disadvantages to a tattoo is that it can be altered. It will fade over the years, and the cat has to be anesthetized in order to get one. Also some people will not have any idea of where to look for this tattoo when they chance upon a lost cat.

The registries that hold the information are often overlooked when the owner moves residence. With so much going on, it sometimes slips the mind of the owner to let the registry know the information they have is out of date.