Animals have been getting tattoos/brands for years. Usually it’s while they are awake and it’s a needle gun jabbed into their skin while they are restrained. Or it’s BURNED into their hide from a branding rod. Awake and restrained. It’s common to tattoo animals for identification on farms and other places.  There are worse things that can be done to a cat than giving it a tattoo. In my opionion, a spay, neuter, or de-claw is WAY more destructive traumatizing than giving a cat a tattoo while it’s properly sedated. I am sure he took care of the tattoo while it healed and the vet probably suggested pain meds to control pain during healing. The cat looks happy and healthy however, unfortunately, resembles a Ed Hardy douche now.  While this is strange and not “accepted” how he did it, he looks like he had the cats best interests in mind. The vet? I don’t know. I would question her sanity for going along with tattooing a cat.. LOL However, we do more traumatizing things to our cats/animals everyday. This is just strange and weird, and I am not saying I agree with it but I think he really loved this cat and wanted to share his art with it. He didn’t mean any harm to him/her and people are freaking out over nothing.