Onomatopoeia for sirens (police, ambulance, fire engines)

I came across these two sentences in Peopleware

The Furniture Police at one company we know even listed a number for spilled coffee on the Emergency Numbers decal affixed to every phone. We were never there when anyone called the number, but you could probably expect white-coated maintenance men to come careening through the halls in an electric cart with flashing lights and a siren going ooogah-ooogah.

I've never seen ooogah-ooogah written for sirens sound before, but I quite like it.

I, myself, as a kid remember saying something like nee-nore, nee-nore — but I don't know if that's regional or just kiddy speak.

• is there a "proper" onomatopoeia for sirens?

I like the one suggested by the UD:

Wee woo:

• is the sound a siren makes. It is used in jest, to make fun of police cars, fire engines, ambulances, anything with a siren, really. Popularized by short films.

Anyway I don't think there is an 'official' one.

I believe you are correct in your original thought that nee-nore is the correct answer, though it is more commonly spelled nee-naw. From Wiktionary:

Imitating the sound of a siren on a vehicle used by emergency services.

The quotations provided illustrate this usage nicely, for example:

Whenever an opponent went down, be it genuine or feigned, the West Ham faithful would simultaneously cry 'Nee-naw, nee-naw, nee-naw, nee-naw', mimicking the sound of an ambulance.