This is quite a vague question, but i’ll try to give my two cents worth.
So, he smiles at you a lot, and he is a Scorpio. Why not just try smiling back at him. Are you expecting something to happen between you both? Like are you interested in him? Do you want him to be interested in you?
I'm not sure what kind of personality you have, but I bet it's pretty awesome :) There are soooooo many reasons why he is smiling at you, so truly, I can't give you a correct answer.
All I can say is, go ahead, try smiling at him and perhaps you’ll get your answer there! Just go with confidence!