There are plenty of signs to recognize a gentleman. The trick is knowing how to spot them.
The signs of good upbringing are sometimes counterintuitive, and those are the ones I find most charming!
An example of etiquette that is still practiced today, which most women know but which escapes many men: stair etiquette.
When a man takes the stairs with a woman, he should, in principle, go up first. The same applies when going down the stairs; he should also go down first.
This is counterintuitive, since gallantry would seem to suggest that the man should let the woman go first.
But if the man has to go first when going uphill, it's so he doesn't find himself staring at the lady's backside the whole way up, more or less forced to look at it. Everyone would be uncomfortable…
On the other hand, when going down the stairs, the man must stand in front of the woman, in case she falls, so that he can catch her (this dates back to a time when women were more likely to fall, because of their shoes and their clothes).
That being said, reading these behaviors obviously requires some practice and a discerning eye.
How can we distinguish the man who walks in front like a boor from the gentleman who takes the lead out of politeness?
It's all in the way you do it. The gentleman pauses before passing the lady, a moment that allows him to acknowledge his awareness of his actions. In the past, a gentleman would murmur, "If you'll allow me..." before passing the lady on the stairs.