Lots of different opinions on how to deal with those uncomfortable stares. While I respect many of the ideas, I've always found that friendliness is a better ally than the stereotypical male trait known as confrontation.
While it's been several years since anyone has given me "the stare," my approach has always remained pretty consistent: SMILE. Direct eye contact. Slight feminine head tilt. In a friendly, non threatening and the most feminine voice I can muster a simple "Hi!" or "hey!" Similar to how you would greet a dear friend.
For those who are staring because they "clocked" you, many are thrown into doubt. That's usually the last thing they expect from us, and a passable voice just confuses them even more. Beyond that, I've also had experiences in which my friendly demeanor prompted the person to speak to me, in one one case because I looked like someone they knew, (my mom, LOL) and in another because we had mutual Facebook contacts and were actually FB "friends" who had never met in real life.
