Have you ever noticed that the
BBC always writes NASA as Nasa in its news reports?
tn207 had, and decided they must have a policy that if an abbreviation is pronounced like a pronoun, then it should be written like a pronoun. So NASA becomes Nasa, but the BBC remains the BBC. I decided to test this theory with NATO and the theory seems to hold, the BBC write it as Nato. So they must have such a policy, and are quite consistent about it.
It seems wrong to me though. I'm sure that at school we were told to write abbreviations as capital letters followed by full-stops like B.B.C. unless the abbreviation spells out a word such as NATO, where you don't include the full-stops. I also think we were told if the abbreviation was a common one, like BBC, then you skip out the full-stops too.