If you want to spare yourself some grief all down the line for the rest of your life, then just be honest to yourself and any woman you meet. She is letting you know the door is open. If you feel you want to get involved a little then just be nice and smile back to her. Start a simple conversation and see where she takes it. If the picture becomes more clear to you then decide if you want to take it personal and go on a date. At this point its all really harmless to you and to her. You don't need any clever or comic pick-up lines and if you stumble a little along the way its okay. We all did/do that. Life isn't so difficult if you approach it in the right way. Good luck.