I had a similar experience I was with my friends in a table waiting for the food, we were talking about stories at work and then my friend said that had this girl looking at me and maybe she was interested in me. I thought it was not for me because my friend is more handsome than me so i didn't took that serious. few minutes past and i look at her and she smiled for me. I had no reaction because that doesn't happen often. I didn't had guts to go talk to her so i continued to talk with my friends and then she left. I regret that day so for the next time someone make this again i will not ignore the sign, i will aproach and say whatever comes to my mind regardless of the rejection.