I think kissing him might not be such a great idea. It's even worse than asking him out in my opinion, as in it's more extreme. If our babygirl here doesn't even want to ask him out, how do you expect her to kiss him?

Anyway, back to the question. I think shy guys usually give A LOT of eye contact to the girl they are interested in. Usually the guy would just look at the girl he's interested in and just stare and stare and when the girl looks back his face immediately turns a bright red and he looks back at whatever he was doing. Usually his staring is accompanied by a few friends that are trying to nudge him to make the approach.

Shy guys also struggle very hard to strike up convos with the girl (and usually end up failing so miserably it's sad, but that's besides the point). They would just talk a lot of crap, and usually that's how you know a shy guy is interested since he usually wouldn't want to talk at all if he's not!

That's just from my observation. Good luck with this shy guy of yours! And I agree with HastaSiempre in that shy guys are the sensitive ones. Usually if you manage to get a shy guy to open up, he's one of the nicests guys you can get in the universe