Feral stray cats in the Uk and ireland are notched or ear tipped before release when they are neutered so that they can be checked without needing to be trapped and handled again, also its notoriously difficult to tell if a female cat has been neutered, even if you can handle the cat enough to examine her. Its easier to tell with a tom although the tom, although may not be that happy with the examination. I am not sure if its national or even if things have changed but when we lived in New Jersey, stray cats were more likely to be humanely put to sleep than rescued because of the rabies risk. All pet cats and dogs were required to be vaccinated against rabies and to wear a collar with a disc on to prove it, you could only get the disc from the vet when the pet was vaccinated and it had the issue year on it. Stray animals with no disc were humanely destroyed.