It was designed in 1958 for use at a ban-the-bomb rally by Gerald Holtom, who said: "I drew myself . . . a man in despair . . . put a circle around it to represent the world." It's been used by lots of different causes over the years, and whatever you think of those causes, you have to admit that it's a great logo.
Though I was in high school and college during the Vietnam era, I never wore a peace sign. In fact, as far as I remember, everyone I knew thought it was dumb and embarrassing to wear a peace sign — like the way a hippie would be depicted on TV.