Actaully the motif of a skeleton was quite popular among the WW1 and soon after the Great War. IIRC the meaning of the kind of the emblems was not only the fragility of the pilots' life flying the delicate planes but also personified destructive force and was intended to instill fear among enemy troops on the ground. So the "death playing the violin" emblem was an artistic reference to memento mori motifs and symbolized the terror of aerial combat.