If you have any intentions of adopting this cat then first get a collar with a name barrel and put that on him. That way if he belongs to anyone they will be alerted to the fact that soemone else wants him and will be able to contact you.

I had a very nasty experience a couple of years ago when one of my cats, that I intended to breed later that year, from disappeared. I put posters out but no-one contacted me. A few days later she turned up spayed!! I was absolutely livid as you can imagine. It turned out that she had been "two-timing" for months. Needless to say all my cats are microchipped now, including the indoor ones!