The Pittsburgh Pirate hat with the P logo is the most popular Pittsburgh Pirate hat that is produced. In Pittsburgh, you see them on people all the time. Even if they aren't big fans of the Pirates, they may still wear the hat because the big P can just stand for Pittsburgh. My husband wears his P hat all the time, and he likes the Pirates, but he isn't a die-hard fan. Being from Pittsburgh, I can guarantee that it is not a gang thing. People from Pittsburgh tend to always wear something that shows where they're from - we have a lot of pride like that.
When I was in California in October I saw people in Steelers & Penguins gear quite a bit. I admit I didn't see a lot of Pirates merchandise, but the Pirates don't have as many fans as our other two teams. Still, people from Pittsburgh travel and take pride in their city, so that's why you are probably seeing the hats.
Born & raised in Pittsburgh