Most Helpful Guy
The more needy you look the more unattractive you'll seem to them. So don't look for that stuff. Also if they see you looking they may not want to meet your eyes - may feel awkward to some people.
Girls are usually in their own little world. You shouldn't put too much thought into it. If you see a girl smile and laugh and look towards you... does she think you're cute.. or is she mocking you? See? Don't think about it. If you want to know if she's into you - approach her and introduce yourself.
There are no reliable signs. You just have to take a chance.