That might be them saying they support the liberal agenda, and it might not be. While likely started by liberals, the peace sign on clothing is merely a style right now. They put it on a lot of clothes, and kids, teens, and even adult women wear it. I just saw it on a sweatshirt at Target today. While the sign was originally used by and still used by liberals and hippies, a lot of people who wear clothes with it on are just looking at it as how someone might say “Peace” to someone and/or just think the clothes are cute.
If someone wears a peace sign and isn't fully aware of all its symbolism, that's great in that I know they're a moron before I even talk to them.