I had my kittens Neutered today well they also trimmed their nails and they got their rabies shot. As I was leaving the vet tech. asked me if I wanted their ears tipped. I was clueless she said thats incase they get out and a animal shelter picks them up they know their neutered. Well my kitten will be indoor only cats so I said no. When I picked them up today they have blue tattoos by their lower tummys to show they been neutered. Is this a normal practice?