The wrists thing is an old tip from here on how to get a man to make a move, when he's being reticent. It works, apparently, although I have no idea why.
I think it all depends on the man, and the friendship. Sometimes you just have to say 'would you like to go to bed?' and suddenly he'll realise that it's not impolite to take things further.
I was at a conference today for work, and there was a woman there who caught my eye. She was attractive, looked at me and smiled. I smiled back without wanting to seem creepy. I was watching the talk and talking to a colleague and when I glanced round again, she was looking at me, and again smiled.
So I checked, and she had a ring on her ring finger, however it was a black stone - not sure if that means anything.
At lunch she comes over to talk to me. She's a recruiter, do I have any vacancies.
So. I do, we chat business, she gives me her card.
Now is this a woman who's doing business and being friendly and professional, or someone flirting a bit. I don't know. Women often flirt a bit as part of their work life anyway. Men do too.
Signals are a bugger.