F. A. B. was an utterance delivered by the heroes of Thunderbirds, as a general term of acknowledgement - rather like 'Roger' or '10-4'. Despite its acronymous nature, it didn't actually stand for anything at all (not even 'Fast and Bulbous'). Instead, it was a spelling-out of 'fab', which was in turn an abbreviation of 'fabulous', much used by The Beatles.

Gerry Anderson repeated the idea in Captain Scarlet, although in that case the signal - 'S. I. G.' - stood for 'Spectrum is Green'. As 'Your Sinclair' magazine pointed out, this was incorrect. Sinclair Spectrums were either black or, in one case, grey. That was a pun, 'case'. It has two meanings, see? In this context it can mean 'instance', and it can also mean 'enclosure'. Yes.