I met a woman once who kept laughing and touching my knee while we talked. That's a pretty obvious way of sending a signal to any guy, I would think. But usually those kinds of girls aren't Chrisitians. She must have thought that I was really dense, or something, since I ignored it.
I give out inadvertent signals. I'm normally friendly/polite with any girl, but if I like her in some way, I'll tend to get nervous around her, and find that I don't have a whole lot to say. If I have something in my hands, I'll fiddle with it, put it down, pick it up, move it, move it back again, pick it up, put it away, take it back out again, etc...it would be obvous that I don't know what to do with my hands. I'll be indecisive. It's also 10:46 p.m. I'm going to bed.