Ask him to hang out sometime, and when you're alone tell him you like him and you'd like to explore a relationship with him. Ask him out on a date with romantic intent. It may sound awkward, risky, etc etc, but it really is the best way to go. It is how adults communicate and leaves no ambiguity. Sending someone signals in the hopes that they notice them is usually a waste of effort and time.
If he dislikes you, he'll say no. If he likes you, or doesn't have an opinion of you, he'll likely say yes. Most boys would be absolutely ECSTATIC if a girl came up to them and asked them out. It rarely happens.
If you guys already know each other and are friends, that's all the better, because you're already comfortable around each other. If he says he doesn't want to have a relationship with you, things will not be awkward unless you make them awkward. If he says no, you can move past it and continue being friends.