Originally Posted by AlienQ

Thing is...
Girls that are interested in just sex wont stick around much and if you do not take the initiative to get to business she will move on quickly.

The only hint they give off is Eye contact and a compliment. Those are the only two that have pretty much been sure fire and consistant at least for me. If They do both those things in a casual place you got game.
Small compliment, or big compliment. Either one is the sure flag and from there you got the ball in you park.