[subandi]

https://en.m.wikipedia.org/wiki/NATO

It kinda is common knowledge though, the French version is right on the official flag and displayed all the time.

[ziddoap]

I don't have the flag memorized, and wouldn't know to look at the flag unless I already knew what the acronym was.

[jorvi]

Given by the confusion in this thread and it being literally the first time I have ever read of heard of the acronym “OTAN”, I’d go with not-so-common knowledge :)