drama

So on Friday morning I opened the door and called for one of my cats which I let outside and this stray cat came running right inside of my house. I figure he had to belong to someone since he was so friendly so I took him in for the weekend and put signs up saying I found a cat. No calls. So last night I put the cat back outside and now he is hanging around the front of my house and wont leave.

What should I do?