According to WikiAnswers.com the easiest way to tell if a girl likes you is if she starts blinking a lot. Another easy test is if a girl laughs and touches your arm when you tell jokes that aren't even funny. Sure those are easy signs but I prefer a challenge which is why I always tell attractive girls that I'm wearing my favorite "happy pants" today. If they respond positively to that statement I know it's on like Megatron.