[__rito__]

OK means: "On Kerosene".

See: https://trucksfloor.com/en/blog/horn-ok-please-on-indian-tru...

[muststopmyths]

I would love to see a reliable source for this. All I have ever found is people on the internet asserting this to be true, but no actual evidence (in the form of contemporaneous pictures or documents from WW2).