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					Originally Posted by  Modeldad
					 
				 
				Thought that spiral was ground crew warning had been discounted long ago based on Ultra reports noting it as a mid-late war recognition for fighter aircraft. 
			
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 The ULTRA decrypts that I found and put online can certainly be read that way:
http://www.ghostbombers.com/markings/inv1.html
http://www.ghostbombers.com/markings/inv2.html
Although it would be nice to have the original German wording, taken together the various messages seem to speak of 'additional' and 'recognition' markings pretty much in the same breath, in essence anything beyond national markings and a tactical number. I may be splitting hairs here but the fact that German aircraft are recognisable by a spiral spinner doesn't preclude the spiral being a safety feature peculiar to German aircraft.