How he treats his mother: The way a man treats other women, his sisters and especially his mother will speak volumes about the kind of person that he really is. If he treats his mother with disdain, chances are he doesn't know any better. If he does not have the know-how or the finesses to be gentle with a lady, he will not be able to pretend for long. Look at it this way, gentleness is not something that you can copy overnight; you either have it or you don't.
How he drives/behaves in traffic: Have you ever watched how some drivers behave on the road? Some are so uncouth that it makes you sick. If a man gets really upset and nasty on the road, even for minor offences and if he is always rude and boisterous to other motorists, how can you overlook this? The character that one displays when he/she is angry is a good indicator of the type of person you are with.
How he solves conflicts: A gentleman should be able to solve conflicts without exhibiting any rude or disrespectful behaviour. He should be able to listen, communicate and understand, even when dealing with disagreeable subjects. If he is going to rant and rave, or get mad and ugly just because he is annoyed, upset or working through a conflict, you tell me, is he a gentleman?
How he speaks: Listen carefully when he is speaking. Does he bad-mouth others? Does he uses foul language without any apology? Are his words cold and icy or are they warm and gentle? It is "from the abundance of the heart that the mouth speaks".
How he treats people: How a man treats people in general will definitely point to how he will treat you. Why should a woman believe that a man who is disrespectful and rude to others will be respectful to her? If a man shows you from all angles that he is not refined, and if he is being less than a gentleman to others, then please, like the Jamaican adage says, you should "take sleep and mark death".
How he grooms himself: A man's general grooming style says a lot about who he is. Look at how he keeps himself; it doesn't take lots of money to be neat, clean, and well groomed. A gentleman will take pride in his grooming.
How courteous he is: Does he say, "Please", "I am sorry", and "Thank you"? These are words and phrases that we are taught from kindergarten, yet it is amazing how many people don't ever use them. A gentleman should have these as a part of his vocabulary, and he should use them appropriately when necessary.
How others view him: This may sound like a simple matter, however, it is not. If he is a gentleman, you are not the only person who should know. Others should be able to tell as well. If he is crude and mean-spirited, he may be able to hide it from you for a while, but trust me, those looking on from the outside can help you to know.
A word of advice: Don't pull out your hair trying to find out if he's a gentleman, just open your eyes and look, the signs are there.