If you're not gonna hit on them, be the one sending hints. Guys, at least I, kinda need some very obvious clues for them to try it on other guys. So stare, smile, whatever, make sure that they know you're interested.
And if you're certain someone's looking at you/likes you, just force yourself to be brave enough to approach them. Worst thing that can happen is a rejection - and nobody is above being rejected. And even if you were to be rejected on a superficial level, at least you know he ain't worth it
