Purdy, if you're worried about cats in your area that may be strays, have you tried fitting your own collar to them with a message and your phone number?
Paper collars are the advertised method, but I keep one quick release collar which has my name and number written on the inside and the word "LOST?" scrawled on the outside. I've successfully identified one real stray and one psuedo stray with this method, so know it works. We have a LOT of well-meaning cat lovers around here and as a result, lots of strays also are attracted to the village as they get fed (not by me I hasten to add unless the cat is clearly suffering). It does get quite confusing.
One of my boys, Theo, quite frequently turns up with someone elses collar on, as he's a wandering soul with big eyes, a limp, a fondness for children and a soul wrenching meow
He hates wearing collars though and has worked out how to wriggle out of the quick release ones I put on him so thats not an option. As a preference, though, I don't collar my cats. Having seven of them is a cost implication but also as they are all chipped and established here I don't see the value to what I perceive an added risk (we have had safety collars fail to release). Also, my old lady Pursley has a bald ring right around her neck due to wearing nylon collars in her younger years. It's handy for applying flea treatment but looks bad and she can scratch her skin with her back claws which worries me.
Chip scanners are only one step. When cats with chips get lost, only vets are allowed access to the database company linked to the chip, so you'd still have to take the cat to a vet to determine if it is local or not. Some vets have lost and found books for local owners, so they would possibly recognise a lost cat you took in even if it wasn't chipped.