5-O 

5-0 became a slang term for law enforcement (aka police) after the hit show "Hawaii Five-O". The show was centered around a fictional division inside the State-Police of Hawaii and carried the same name as the television show ("Hawaii Five-0". The division's name gets its origin from honoring the fact that Hawaii was the 50th state to become apart of the United States of America.
On a side note, the division was actually called "Hawaii Five-0" (as in Zero, no the letter "o") but IMDB has the show listed with the letter "o" in the tittle.

The Five-0 (5-O)had set-up a speed trap and gave me a hefty ticket!

5-O by RichieV April 19, 2007

5-O 

5-O goes back even further than California late 80's. It's origins are a reference to an old 70's TV show called Hawaii 5-0 starring Jack Lord. The police were 5-O and eventually the show lingo caught on as hip among petty criminals in southern California.

"STOP, Hawaii 5-O!!!!"

....blah, blah, blah- small struggles, throw a few punches - handcuffs criminal and stuffs them in the back of a patrol car ....

"Book 'em Danno", said Steve Garrett.

5-O by ex-wife of 5- Oh April 26, 2003

5-O 

5-O, commonly written as 5’O, 5’0, 5-O, 5-0 is a slang term used by a lookout committing a crime with a group to signal that officers of law enforcement are arriving. It is commonly used by skaters who skate in groups to tell everyone to scatter.

5-O pronounced as five-Oh is the combination of the number 5 and the number zero which throughout time has been pronounced as “oh” (O). It originated from the 1968 police tv show “Hawaii 5-0” where the 5 and 0 represent the fact that Hawaii was the 50th state.

“Shit there’s cops coming”
“5-O 5-O!”
“Run!”

5-O by Danny Despacito June 2, 2020

5-O 

police, the cops, po po

yo, it's 5-O
chill man we aint da 5-O

5-O by dbam December 28, 2005

5-O 

a patrol car.

Orgin: late 80's Cali.

back then all police cars at one time where Mustangs, 5.0 engine model, on the front and side of the car it read in chrome letters the engine model. 5.0.

it refers to the car they patrol in.

now it also refers to the police officer himself.

"5-O keeps making rounds through my neighborhood like we are causing problems".

5-O by Lec2 February 9, 2003

5-O 

A patrol car. Back then all cops in parts of the California district drove 5.0 engine Mustangs.

They threw him in the 5-O now he doing 25 to life and trying to survive yo.

-Tupac song

5-O by Makaveli Shakur November 3, 2007

5-O 

The police. 5-O is the type of engine that police cars use.

"Hey lets get the fuck out of here the 5-O is coming!!"

5-O by Vivianna April 3, 2008