Of course if you could catch him, he may have a microchip which will identify his owner. I will keep a close eye out for him too and see if he will let me approach him because another trick you can do, if the cat is agreeable, is to put a paper collar round his neck with your telephone number written on it and a message saying call me or I will trap him and have him rehomed, that may get a reaction. He doesn't seem to come into our garden anymore, but like you I have seen him out in freezing cold weather on my way to work very early in the morning. He is either a tough boy and likes his freedom or nobody cares for him.