My babies have ear tattoos.
When I had Chynna spayed in 1993 I don't think there was microchipping: just tattooing. For unfixed cats the tattoo is inside the left ear. For fixed cats the tattoo is inside the right one.
The tattoo is a combination number/letter that is unique to me and my kitty. My name, address, phone number and kitty's name is attached to this number and is on file with the local Humane Society. When I move I have to update the information with them just like I would with a doctor etc.
Abby also has a tattoo in her left ear.
With Chynna I wasn't asked if I wanted her to have an ear tattoo, it was just done because she was spayed at the Spay and Neuter Clinic and I guess that is their standard policy as they are affiliated with the local Humane Society. Unfortunately the tattoo wasn't put deep in the ear so it's visible when you look at my pure white kitty
and it's not easy to read because the person who did it made a mess of it.
When I had Abby spayed I took her to the vet near my home instead and I did request a tattoo with her. It was put deep into her ear and you can only see it if you fold her ear back, and it's easy to read.
I don't know if I like the idea of a microchip. At least with a tattoo it's visible and anyone can see that the kitty has a family and will likely contact the Humane Society. With a microchip it's invisible and I don't know anyone who walks around with a microchip reader in their pocket, so any cat that is on the street and seen looks like a stray. I know so many people, including me, who have found a stray kitty and taken it home and either adopted it or found it a new home. I'd hate to think that I rehomed someone's cat because I couldn't see an ID tag.
In the future if I get another cat I will also get her/him tattooed instead of a microchip, just because I think it's a better system than sticking a foreign body into the animal and because it's readily visible to anyone who looks at the cat.