Why are the police called the 5-0?

Answer 1

5-0 became a slang term for 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.

Answer 2

Its a reference to a 70's TV police drama called Hawaii 5-0.

The actual title was Hawaii Five-0, named in honor of Hawaii, the fiftieth state. See the link below for the promo for the new CBS revival of Hawaii Five-0 scheduled for the fall 2010 season.