Oh yano, we're having drinks and suddenly find ourselves having sex. I know it's subtle but I take the hint they think I'm hot then.
If you look at them and they look away, if they blush around you, or if they get fidgety (like playing with jewelry,hands,etc) when they look down alot if they're a nervous person, or if they look straight into your eyes if they're not nervous,also if they bug you alot :)
I wouldn't have the foggiest idea.
When you both try to spend time together quite a bit, crossing glances quite a few times, smiling, texting on a regular basis.... uhhh...thats really all I know=p