Sorry, Jim, but I can't warm to the Cross of Agadez as being the stylistic parent of The Mark. The Mark is too sophisticated to be its derivative.
While the Cross was relevant to the Tuareg people, it was likely meaningless to the Sudanese, the source on most of our Marked kaskara. Also, the Mark appears exclusively ?? on imported German trade blades so Hausa smiths likely would have had no contact with them, and the Mark was skillfully engraved likely by a silversmith, not a blade maker.
My best origin story is the Enigma mark is the emblem of a sufi order/tariga common among the Tuareg and Sudanese of the Nile Valley. The emblem would be known among silversmiths of both areas so that it could be reproduced virtually identically over a wide geography. Maybe the Qadiriyya, active in Morocco and the first sufi order in Sudan. The link shows their emblem.
https://en.wikipedia.org/wiki/Qadiriyya