What behavioral signs do you observe in people?
I think we are the type with a very keen eye on this stuff, so let's share our findings.
They could be verbal signs (the way people phrase stuff) and, of course, non-verbal signs (body language).
Now, I am not looking for the typical ones you find in any book on the subject (pupil dilation, folded arms, "watch the feet", ..). No, I am more interested in a page out of your personal diary; more unique traits that you find interesting and/or have proven helpful in your own life.
I will start off with 'The blink'.
Quite a theoretical one, I know, but in my experience one of the most reliable ones -- as, perhaps, it behaves as a micro-expression (almost impossible to control), while it displays itself in a very obvious way.
Advice: Whenever you see the see the blink, you can be pretty damn sure the subject did not like that question.
Of course, the reason why will often be obscure, but you do have your information that some aspect of what you said caused little to extreme distaste to what you said.
Great example happened during a date:
We were discussing her job (pharmacist) and it turned out that, X amount of years ago, she had moved from one pharmacy at village A to a different pharmacy at village B. The natural question followed, I asked her: "Why?"
The answer came quite hesitantly (verbal sign on top of blink), telling me facts like "distance" and "travel", which in truth were half-answers at best. And at the end of those awkward lines she dropped some sort of 'conclusion': "Yes, that's, actually, the main reason..." (verbal sign 2? -- something to do with trying to convince?)
Seeing that it made her uncomfortable, I dropped the topic.
So what was this discomfort about? 3 .. 2 .. 1, no more bets.
She later confessed that, at the time, she went to move in with her boyfriend (now ex-boyfriend).
And on top of that (the subject she was desperate to avoid), it turned out she still lived with the guy, as friends, almost a year after they had split up.
(Naturally afraid for my reaction. And also, it showed how much trouble she has letting go.)
Example number two:
At a restaurant just yesterday, I asked for 'the plat du jour'. Owner told me "vegetarian lasagna". I blinked once. Didn't hate it, but the "vegetarian" part was a slight turn off. The owner perhaps subconsciously answered to 'the blink', recognizing it didn't look like my absolute favorite, and proceeded to explain the entire cooking process.
(I did end up ordering one, and it was super tasty. So well done.)