To give someone the finger. Originally coined in the early 1960's in reference to Eagle Rock's many Latino gang members, the expression is regaining popularity as the area is gentrified by white, shallow, self-absorbed thirty-somethings.
I looked in my rear-view mirror and some prick in an SUV was giving me the Eagle Rock IQ sign.
Pejorative reference to Eagle Rock, California (a suburb of Los Angeles formerly known for its largely lower-middle-class Latino population). Derivation unknown, although perhaps related to Yosemite Drive, a major thoroughfare bisecting the area.
I was lucky to get out alive when my car broke down in the middle of Stinky Felix National Park.