IMO, if found with no collar take it home and put in ad in your newspaper/craigslist for 2weeks and list where he was found (don't list specific details like color) list your # and have them ID the dog name,color, etc. Helps to check if the person is legit if you have a white dog and he says its black that tells ya something

P.S.

You can also take him to an animal shelter/vet and see if they can scan his microchip. (if he has one)