Dąbrowski has an unidentified “Symbols of the Ancient and Accepted Scottish Rite”, see below. Judging the text in the triangle, it is from France. I don’t know in which degree of the AASR this image is featured and if there are other systems or degrees with this symbol.
In early high degrees you sometimes encounter something like this:
This example is from a “Maitre Parfait” (‘perfect master’) tracing board of the Kloss collection (84 Tableaux, see here). This pyramid is the grave of Hiram Abiff. The letters refers to the password of the degree, which is sometimes also an L.
The “Maitre Parfait” degree in the Baylot collection also says that:
the pyramids of Egypt, designate the sciences, and refer us to the ways to which the Freemasons should direct themselves
Later in the same Baylot manuscript (“Chevalier d’Orient”) the pyramid is: “the true Freemason who elevates himself up to the highest heaven to worship the holy and indelible name of the Supreme Being”.
Dąbrowski P. 212. Year and designer unknown.