Hmm...if you're *slightly* flirtatious...(emphasis on *slightly!*)...and also just kind of chill...then I'd like to think, though people are more different than anything!!...that most guys would notice.
Just make small talk with him when you can. If somethings going on and he wants to get to know you more, he'll probably invite you, or you can invite him to something.
It's really not much different than just becoming friends. Most guys go for girls they already know in some fashion, (*again, most...not all...), so just take a little initiative, and hopefully he'll pick it up.
Oh wait...too late? *sighs* Story of my life...