The drool running down his chin is a huge sign.... So is him trying to get you to laugh, making "manly" (not manly) gestures towards you. Him ALWAYS trying to impress you. He would try and touch you (appropriately) as much as possible. He "accidently" bumps into you EVERYWHERE. Seriously, some of us could not be more obvious.
He treats you differently then other girls. Always sits around you. Text or calls you first.. Flirts with you all the time. Wants to hang out with you a lot. Might tease you.. ? Does things to get your attention.