Body language is very telling, especially when the person doesn't realize they're doing it. So to answer your question, I suppose it would be how they use their body to attract me, whether they realize it or not. It wouldn't have to necessarily be anything sensual or sexy either, and they wouldn't have to be wearing anything skimpy either, tight, or form-fitting.
Alot of the power of attraction is through body language and it shows people your emotions and temperment through your posture. People that have their arms crossed all the time tend to be people who are impatient, demanding or indifferent about things, possibly scared, and their crossing their arms is like subsconciously guarding their heart. While people who move around while standing in place tend to be liberated people who are either sure what they want from life, are open to new experiences, and while they may be self-conscious, are not as concerned with the world around them and the people around them in a social climate and so don't consciously restrain themselves from acting out their mannerisms, quirks and other nuances.
So to answer you question, I would sooner be tempted by someone who is open to new experiences than to be tempted by someone who is hiding something or seems afraid.
While this isn't ultimately about relationships and the approachability of a person, I can say that I'm attracted (tempted if you will) to people who are confident in themselves and are displaying this boldy by way of body language. I can tell alot from that. And I'm more likely to give quick stares and then look away. I think to stare at them and them to see you staring at them can be uncomfortable for both parties, but its most likely what will cause the two to talk to eachother.
Let me be more specific for you with a hypothetical situation-
I'd really be tempted to stare at a girl, say waiting in line at a bank (and I'm standing behind her), and she's standing there not pissed off or shit-faced like some people are. She has this smile on her face, is swaying her hips back and forth, tapping her foot to some beat or tune, and is humming gently to herself.
Its like everything else would be drowned out in a moment like this. Can't help but stare in near admiration for a complete stranger.