I heard it came from some battalion in WWIIThe BPP took their name and symbol from an organization Stokely Carmichael formed in Alabama in 1965, which Newton and Seale learned about when Carmichael came to Berkeley in 1966, when he was still in charge of SNCC. That meeting is also generally thought to have the first use of the term "black power".
Apologies if I'm coming off as harsh and know-it-all, this is just a topic near and dear to me and what I research.
Heres a link to some information about the Alabama organization:
Lowndes County Freedom Organization | The Black Past: Remembered and Reclaimed