There are times once we might see a stray cat wandering round the neighborhood and climbing all over the cars. Frequently these may really irritate us - but what comes about when one of those cats carries a collar? That is an indication they have lost their way and somebody out there may be searching for them. Which means you have to find the better way to bring them back to the worried owner.
The first thing you will have to do is bring them into your home or at least into the garage or enclosed porch. You want to make sure they don't bite or scratch you. Who knows how long they have been lost and what form of problems they might have contracted.
Offer them a bit of food and water so they are going to be well fed. This will even make them feel better about you taking them into your home as well as getting anywhere close to them. Just be sure not to offer them cat nip of any sort. It's possible for them to get crazy on something similar to this.
Next you need to set up simple signs around your neighborhood and the city which you live in. Put up a picture of this cat plus your phone number. Tell them that you are trying to find the owner - but don't put your address down. This is never a secure thing that you can do. Try to search on the collar to make sure that there is no number or address on it.
A lost or found cat is not always a simple thing to return. If no one calls up after a couple of weeks you could keep the cat. If this isn't an option than provides it to the humane society or the pound.