What is the correct form of address for a police officer?

Solution 1:

They are all officers of the law, so "officer" applies no matter what their rank ("Pardon me, officer...").

Solution 2:

I've lived in Britain all my life, and I don't think I would use any particular word to address a policeman. It's seldom necessary to use an appellation in a typical British conversation. Indeed, it would seem odd.

In the US, people seem to like calling each other "Sir" and "Ma'am" as a mark of respect, and I see no reason why that wouldn't be appropriate with a police officer.

If you must use an occupation-specific appellation, then you can use the person's rank. But that requires you to recognise their badges, or you risk getting the rank wrong. AS @Gnawme observes, "officer" is always OK.

Any policeman worth their salt, of course, will treat you politely whatever you call them (unless you abuse them).

Solution 3:

When in doubt, ask. This sort of thing does vary from one region to another. When you find yourself in a new place and you're not sure what the local custom is, there's nothing wrong with asking politely: Excuse me... I'm new to this area. How should I address a police officer such as yourself?

Solution 4:

I don't see the harm in calling them 'constable'.

Solution 5:

In Japan, we adress police officer just casually as “Omawari-san" meaning "Mr. (Ms) police (officer),” though I’m afraid I’d be laughed at when I did so in UK and US.