I love Val's collar & tag idea!
But sometimes cats will get in cars w/open windows and can get pretty far from home. Try also calling the shelters to submit a found pet report - and in our city, the newspaper will post a "found" ad for free. Don't be overly specific with the ad description, though - leave out some detail so you can identify the real owner if you get any calls.
First and foremost, as mentioned by others here, before you introduce any stray animal to your pets, get it checked by the vet! Wash your hands before you touch your pets after you've handled a stray, too. I picked up a kitten on the freeway once that was loaded with fleas & losing hair. I thought she was losing hair because of the fleas - but it turned out to be ringworm!
I spent the next TWO YEARS & a ridiculous amount of money to get rid of that horrible fungus, bathing, dipping & medicating ALL of my cats, cleaning the house top to bottom every week, too!
All of the feral care tips here are great - you guys are so wonderful to take care of them! Think I'll try the covered bed idea for my one little feral - she has a snuggle tunnel, but yours sound nicer.
Many years ago, I was reunited with my dog who was stolen out of my yard after she had been missing for 3 years! It was a small town, and the shelter staff knew my new address & phone even though I had moved. When the shelter called me because she still had her old tags on (!) I said "What dog? I don't have a dog!" before they described her to me. I was sooooo happy to get her back!