When a guy drives past in his car slows down looks at you and smiles does this mean he likes you?

It could mean quite a few things. Of course it could mean that he likes you and maybe is to shy to stop and say hello. It can also mean that he wants something from you, such as sex. It could also mean that maybe he just thinks that you are a pretty girl but doesn't stop because he either is married or has a girl friend. And I am sure that there are plenty other things it could mean. If you find him attractive then you should wait for him to approach you with conversation. If he likes you then he will approach you if he has nothing to hide and if that is what it means. But if he keeps riding by and just smiling take it as it is just his way of saying hello but I am attached. good luck