[Jim McDougall]

Ongoing,
So it seems we have established that the enigma mark was known in the period around WWI by the Tuareg, and it seems in the Air (Ayr) regions of that massif in Niger centered around Agadez.
The three examples cited in Briggs (1965) represent takouba of two Tuareg chiefs and one figure of nobility of these regions.

At some point, this same device began to occur on kaskara blades in the Sudan with one primary example mentioned by Ed as to the Judge al Shengeti c. 1956 as seen in library at Khartoum in 1961.
There seem to be several other kaskara without exact provenance with the enigma placed in similar rendition and placement that exist.

I recall Iain years ago suggesting this resembled a lock/key known in Sahara to be used by Tuareg, and in 2016 it was suggested again that this might represent a key.
With this idea, it seems quite possible that this device might indeed represent a key, perhaps used metaphorically representing possibly an achievement or status relating to Sufi following, and that would have to do with individuals with profound standing that had reached it.

More to consider I guess, and the search goes on. I'd like to finally get this solved 'this run', recalling similar discussion/investigations in '08/09, '16 etc.
Whatever the case, glad Ed brought it up again here.

The bottom image is that of the Shengeti kaskara; I noted also in the 2016 discussion there was an apocryphal suggestion that this mark had been seen in a reference where it was noted as British. With the existence of this device in Tuareg context in 1916 I am inclined to think otherwise, but place the note here as inclusive for consideration.