This is from a TV soap opera.
He works at a grocery store, first time I saw him, he smiled, I smiled back. I didn't think of it much but the 2nd/3rd time I went, he was staring at me and smiled when I saw him. But the way he looking was like he was waiting for me?
He probably smiles at every one. If it really interests you observe him and make sure he doesn't notice you does he smile at other people?If he doesn't he probably thinks your cute or something if your interested in him say hello or have a short conversation.
The smiling is probably attributed to being polite .. The staring may be attributed to the eye contact you are initiating. If he hasn't made any other "moves" to get your attention or to initiate contact with you .. It could be attributed to either his shyness or the fact that he's simply not interested in persuing .. Only looking.
Given the staring, I'm guessing there is something about you that he considers attractive.