I have seen quite regularly student grade Hungarian violins (made in 1970s?) with two piece backs that had fake flaming on them. The flaming was sprayed on with some sort of masking, but so poorly done that the faux flame from one side that should have stopped at the middle seam, slightly overlapped onto the opposite side of the two-piece back. Dead give away!
I have seen fake flaming on old German violins that must have been done with something chemical, as the wood was burned such that there was a groove in the wood and the varnish that was originally on the top of the "flame" had completely deteriorated. Or perhaps....
I had been told by a luthier who had trained in Germany back in the 1950s that some of the faux flaming was done by tieing string/rope around the backs and burning the rope.