Not My Cat stopped by for a treat

After disappearing for a long while, Not My Cat is back. I'm starting to suspect that he might be a stray because although he looks outwardly healthy, I've stroked him and he's very thin under the floof. He's also unneutered and has a limp that suggests he might not have seen a vet in a long while. I'm trying to earn his trust enough to take him to a vet and check for a microchip.