I do not know....
I’m curious as well. Certainly SAM as a prefix is a bit more interesting than the “NA” callsign.
BTW, as fake potus/vpotus callsigns go, when using SAM, I’ve seen various numbers used besides 46.
~~~~~~~~~~~
I’d been looking at mil aircraft today and I saw SAM as a more recent designation for a class of aircraft - SAM (Special Air Missions)