Was it red? I read an article that said guys from the West Coast use the Red Nats hat as a sign of being in the Blood gang.
Not that I am a gang expert, but I have known some, specifically some that went to Poly. Most Poly kids are affiliated with some set of the crips, not bloods.
I also haven't seen any 'extra' red National hats around. I guess the W would supposedly represent West Coast, but I haven't seen too many. In fact, I see a lot more blue National hats than red, no matter what city Im in. I live in Orange County, grew up and spend time in Long Beach, and work in LA.
There is a gang in the city of Wilmington that wears blue Nationals hats to represent their gang though. I work for the post office in a city a few miles away, and one of the dudes I work with let me in on that one when I wore the blue one to work one day. Didnt really ask specifics though.