Can mean 2 things in the Bay Area: one, can signify cops, police etc. two: can signify the 1984 to 1991 ford mustang 5.0 nicknamed 50 (fifty) mostly used as a sideshow car or a cheap getaway car when pulling licks.
Example one: Shit we got 50 following us!!
Example two: That nigga big murf's 50 go dumb at the sideshows whaa!!!