This all depends on the context. Am I out with my friends? If so, I interpret stupid conversation like "so where are you from," or "I've never seen you before, who do you usually hang out with" or anything along these trivial lines as sexual interests to SOME degree. If I'm at work I'm gonna interpret it as small talk. It's all about the degree to which they show attention to you in relation to the circumstance AND others. For instance, a friendly girl is just a friendly girl. If she's talking to me and everyone else in a really gregarious manner, I'm not going to assume interest. However if there's extended interest in me disproportionate to her interest in others, I'm going to begin entertaining the possibility that the girl likes me.