Depends on the person. Some social people may talk to you or seem focused solely on you. Even laughing at things they wouldn't over-wise (Dark Humor's a wonderful example). Some people are just clumsy/nervous around you. This is another big sign. Shy People may just look/stare at you for a few moments, look away, and then look at you again. Look uncomfortable, move away, and see if they are still looking at you. If not, it's someone else. If so, then move in for the kill. Some aggressive people may just beat/abuse you. If you're being hit for seemly no reason, then they probably like you.