Originally Posted by 
joypulv
				 
			Set your hair on fire?
No, you say hi using his name, as you walk by.  Don't do it coyly or hesitatingly, but with a normal smile.
Do it maybe 3 or 4 times over a week, each time you go by.  If he is interested he will stop to talk or at least say hi back, and you can tell a lot from a hi.