If they come up to you for attention, then they're probably just strays that used to have a home. [Whether they'd have someone come collect them sooner or later, like right now, is a little more up in the air.] Otherwise... food's a pretty good motivator for anyone, really. Just show it you're a safe person who's not going to hurt it. It might take a while, depending on the cat, but either way you'll probably have to do a little work to earn its trust.