You don't. Not only that, you discourage anyone else from doing so either.
The most important thing to understand here is this: You do not have a right to attempt a romantic relationship with every random woman that happens to strikes your fancy out in the world. This shouldn't have to be said, but the preponderance of evidence shows it clearly does. There's a famous video showing excerpts of 10 hours a woman spent walking around NYC, with over 100 attempts to do everything from initiate conversations to out and out harassment. That's over 10 an hour!
Women should not have to put up with this.
Furthermore, one of the most common ways to try to avoid this kind of contact is to wear headphones. So if you see a woman out and about wearing headphones, consider it code for "Please do not talk to me."
There's even an article on this exact subject on Upworthy titled, get this, Advice for Talking to Women Wearing Headphones Ignores Why Women Wear Headphones.
If there's really some kind of connection there, she will take off her headphones on her own. If she doesn't do that, please leave her be.