A collar or other physical appariments wouldn't stop you from abducting it either. Where I come from and (I assume) in many parts of the world, cats have an electronic chip in their neck with basic info about the owner and how to contact them, which would be discovered when you bring them to the vet.

But I think that's more of a cultural thing. Personally, I consider not letting your cat roam free in the neighbourhood (if you have the ability to let them) unjust and borderline animal abuse, close to how I would consider it if you kept your dog inside all the time.

Finally, taking a cat home out of, what, pettiness(?) sounds like a terrible idea, because beyond any notion of ethics, dealing witha cat you keep away from their territory and the people they know would be both a psycological and financial perspective. If you want to be hurtful to someone, there are easier and cheaper ways to do it than to abduct their pets.

So no, as a pet owner, abduction is really not anywhere near being a concern for me. Getting run over though? That IS a concern, particularly when cats panic. However, cats have far better hearring than we do and can hear cars from a mile away (esp when they're familiar with them).