Do they mark the cats if the have been spayed or neutered?

probably, our vet clips the ear tip and some notch the ear tip.

I was wondering because Romeo has a notch in one of his ears

aha! Sometimes that could be from a street fight but you never know! Not all feral cats are wild.

there are all kinds of wild cats here in Istanbul. But I notice that the dogs have been spayed/neutered and have their ears marked.

did you notice the cat's name is Chumley!!

Godtess: yes!