Short for "berries and cherries", meaning a combination or collection of blue and red lights, usually flashing. Can also be used when referring to police vehicles with the lights on.
"Hey man, you better turn off at the next street. It's b's and c's galore up ahead! Must be a DUI checkpoint or a big accident."
"Dude, I'm thizzin' so hard. I'm about to rave out with my b's and c's! You down for a lightshow?"
Driver: "Yo bro, toss that blunt out the window!"
Passenger: "What? Why?"
Driver: "We got some b's and c's comin' up on us fast!"