Generally a blue bandana, most commonly used by Los Angeles street gang known as the Crips.
"You see the blue flag in his left pocket? That's a Crip."
by VQC BK December 18, 2009
Don't want to wear my blue flag in the hood, for fear that a blood might shoot me while suspecting me to be a crip.
by Wutwutwutwutla July 19, 2006