Most Helpful Guy
I mean, I don't think it necessarily means she is explicitly hostile to human interaction. Sometimes I listen to music in public, but I wouldn't be bothered if a cute girl tried to talk to me. She probably doesn't want to be pestered by overly persistant men that she's not intetested in, but that goes for all girls--regardless of whether or not they're wearing headphones.
So yeah, if I was really feeling it, I'd probably approach her. Of course I would try to be tactful and charming, and if she seemed like she wasn't having it, I'd leave her alone.
I mean I think of it like this:
Best case scenario - I meet the love of my life.
Worst case scenario - she tells me to fuck off.
I have a lot more to gain than I have to lose.2