What does S.I.G stand for in Captain Scarlet?

Answer 1

Supermarionation is Go! () the title of a magazine based on fandom of Andersons" works using the Supermarionation process, alternatively, Spectrum ( color code organization- hence Captain Scarlet- all officers had last names of colors- Is Green ( Proceed, like traffic lights!)

* The above answer is partially incorrect. SIG stood for "Spectrum is Green" in the Captain Scarlet TV series, and is spelled out in several episodes as well as in the closing theme song. It means the same as 10-4 or acknowledged. There is also a less-used variant, Spectrum is Red which is an emergency signal.