re: black flag.
they were named panic but there were tons of punk bands called panic, raymond pettibone suggested they use the name black flag, him being a card carrying anarchist and after the black bars design he had made and someone in the band noted (i think it was chuck) that it looked like a flag; they also knew of the roach spray of the same name, so they kept it.
like tons of stuff in their career, there's multiple meanings about flag's name.
after marilyn monroe's last movie before she died, to be more specific.
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after seeing my signature:
metallica named themselves that after a scenester talked to lars about possible names for a fanzine he was putting together, one of the names being "metallica".
earth: after black sabbath's name before they became sabbath.
merzbow: from an artist who used trash to make his artwork, one of his works was called merzbau.