For historical significance, let’s go with Dmitri Shostakovich’s Eighth Quartet:
Shostakovich’s Eighth Quartet has long been recognized by its official dedication “to the victims of Fascism and war.” It is becoming increasingly more apparent, however, that the Eighth Quartet is a highly personal and autobiographical work. Although Shostakovich once claimed that a visit to Dresden in 1960 was the inspiration for the Eighth Quartet, it is more likely that his joining the Communist Party that same year was the catalyst. Shostakovich’s son, Maxim, noted that he had only seen his father cry twice: once when his mother died and again when he announced that he had been forced to join the Communist Party. Shostakovich felt that joining the Party was both a moral and physical death, and for that reason, he presented the Eighth Quartet as his legacy.
Shostakovich clearly intended to personalize this quartet. He infused all five movements with the musical representation of his name, DSCH, or the musical pitches D, Eb, C, and B. Shostakovich also inserts many musical quotations from his own works. Shostakovich explained to a friend, “When I wrote the Eighth Quartet, it was also assigned to the department of ‘exposing fascism.’ You have to be blind and deaf to do that, because everything in the quartet is as clear as a primer. I quote Lady Macbeth, the First and Fifth Symphonies. What does fascism have to do with these? The Eighth is an autobiographical quartet, it quotes a song known to all Russians: ‘Exhausted by the hardships of prison.'”
I may be selling Johann Sebastian Bach short here, since it was from him that Shostakovich got the idea of a musical signature; if challenged on that point, I’ll say I’m going by a Pritchard scale of musical significance.
