Captured soldiers from occupied countries

Hi Indy and crew!
What happened to Polish/Czech or other nations soldiers/pilots that would be captured by the Germans while wearing a British/Russian uniform and sporting a national tab?
In the Czech Republic there is a legend it meant death. You can even see it in the movie Deep Blue World. Just before a combat mission to go over France a guy points to another’s CZECHOSLOVAKIA tab on his shoulder and says "if they catch you with this, they’ll shoot you on the spot. " Just to clarify, these guys are Spitfire pilots.
Is it true?