The WaPo delves into the public restroom stall phenomena:
"From what I've heard, foot-tapping. Online [dating and chats] is another blatant way. As far as the other ways, if you are walking through the mall, someone might make eye contact. If you walk down the street and you see someone you are interested in, you lock eye contact."I think the Craig thing has gone far enough. It's pretty bad.
Then you apply the three-second rule.