Brenda, the tatoo could be from a mass breeder to identify his/her stock
I have a little one that was found wandering in the desert and was dumped there (quessing by the breeder) as she had a tatoo (hand done) in her ear. When I took her to the vet for her spay the vet said she had produced so many litters her inside were a mess...
The one thing you want to check out on chips is who is the maker and what does your shelter/pound carry for the reader machine. It doesn't help you to chip a dog if the places that might find your dog does not have the hand reader. Also, the needle is pretty darn big for the chip. I have always chipped my dogs when they went in to be spayed and neutered but one. I got him out of the pound and had them do it and it was painful for him (he yelped) and he was one 10#'s.
Hope this helps