Im not really sure, I read something on it not too long ago and it was all because a lady found a dog with a tattoo and was trying to get it back to the owner..
I also know a lot of breeders do it still but I cant for the life of me remember how you set everything up so if the dog does get found it can be given back.. there has to be a database or something youd think
"When you truly give it your all, you are not afraid to fail. But rather can't wait to succeed." -Robert Griffin III