When every time yall are a distance from each other in you know he's looking at you.
Also if he stares at you when your talking to your friends.If he's really interested in you he'll pay attention to you instead of any aspect of your body!
About the only thing a guy will do that constitutes a sign is quickly looking away when he notices you catching him looking at you, trying to act like it never happened. Or, if he knows he's busted, maybe give a little smile.
Guys don't really do "signs". We communicate through words and don't really do body language or subtle hunts. And it frustrates us when girls do because a lot of the time we just don't get it.
I usually touch her arm or her shoulder a lot. I have a since of humor so I usually go with some playful teasing. One girl went by "Missy" so I would call her "misty" things like that.