Origin of slang term "Five-O" in reference to police officers

I’ve always wondered about this. How old is this term and where does it come from? Also, is it “Five-O,” as in the word “oh,” or is it “five zero.”
I’m also wondering how, if at all, this ties into the old tv show Hawaii Five-O? In that case, does “Five-O” come from the fact that they are cops, or that Hawaii is the 50th state, or both? Does the current usage of “five-o” predate the TV show?

ever paid careful attention to the sound a police siren makes? 5 Distincts tones can be made out before a long pause…and then the cycles repeats. Hence five-0.

IIRC, “Five-O” is derived from the show, Five-Oh. The Five-O was a fictitious special police force (state Police) that took it’s orders from the governor. I don’t know when/how this slang became another phrase for Johnny Law, the cops, the pol-eece, etc.

The show was “Hawaii Five-0”

“Five-0” standing for Hawai’i’s status as the 50th state.

The Hawaii Five-O FAQ supports BF and BobT:

Same site:

The show premiered in '68. The first cite of the term to describe generic police is in the NYT, 1983, in an article which implied that it was not uncommon and probably used before that ('83) date.

It never existed before the show premiered.

As someone who watched the show far too much as a child, I can tell you that it was always “Five-Oh”. That’s how all the characters pronounced it.

BobT, unless I’m misreading the question (or your response), the issue isn’t one of pronunciation. Certainly it’s pronounced five oh. But a 401k is also pronounced four oh one, typically, even though it’s a zero between the 4 and 1. So the question is whether it’s Five-0 or Five-o.