I'm not sure whether the story is true, but it seems that concern was expressed about the Russians trying to find out about the Concorde's tyre compound.
So at some aerodrome where Concorde was being tested, the boffins went out and smeared some sort of rubber/latex gunk with the consistency of chewing gum on the tyre marks left by Concorde.
Later the next day, it had gone!
I have an image of perplexed Soviet scientists puzzling over whatever it was their spies had brought back - and perhaps not seeing the joke?