A whistle sounding like a bird call used by members of the Crips. Like other elements of gang culture, it is popular with non-gang members because it sounds "cool".
In contrast, the Bloods have "brrrrat" and "BLAT", both onomotapoeia of gunshot noises. The Crips also have "clat" or "ccclat", which are also supposed to sound like gunshots.
A young black male was shot down in the hallways of a high school after he gave a high-pitched whistle which was misheard as a gang call, the Crip whistle.