Hand touching is such a lesbian thing to do. Think about it. How many times have you flirted with a girl and subtly brushed your fingertips across hers? How many times has that cute girl at Starbucks let her fingers linger on yours as she hands you your coffee? What about the intense interlocking of hands before making out with your new girlfriend? You know, with the little power struggle that ends up with someone pressed against the wall?
Hand touching is one of the most discreet ways to flirt with another woman. If your gaydar has failed you (or you like flirting with straight girls...and hey, who doesn't?) then your "victim" is unlikely to think much of it. If she even notices then she'll probably assume it's an accident. And if she does notice, well chances are it's because in the past she's done a little hand touching herself. Throw in a little eye contact, a smile, a wink, whatever it is that you do, and you should be able to make your point. If you've never heard of this you should try it. Specifically if you work in an industry where you would hand something to someone (money, food, clothing) or you can find a way to pick up something that your crush has dropped.
Bonus: Guys don't know about this. I don't know if they missed the memo or if it's just too creepy to have some random guy touch your hand but the only man who has ever touched my hand in a flirtatious manner was some weird salesman...