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”.
Interestingly, the “Maitre Parfait” degree in Cayers Maçonniques specifally speaks of two pyramids:
Q. What do the two pyramids signify, which are on the Tracing board?
A. They represent Egypt, where the sciences have taken their origin.
Also the Francken Manuscript speaks of two pyramids in the “Perfect Master” degree. They are even specifically placed on the tracing board:
Q. What do the two pyramids on the draft represent, the one being in the south, and the other in the north? and what signifies the figures on them?
A. Those pyramids represent Egypt, where the sciences were much cultivated, and some of them had their origin – on the south pyramid is drawn a meteor which guided the masters in their search for the Body of our Respectable Master H. Abif, and on the north pyramid is the perfect Masters Jewel represented.
I don’t believe I ever saw a “Maitre Parfait” (-type) tracing board with two pyramids. Not even on the image for this degree in Cayers Maçonniques! What is somewhat common, is that the pyramid here does not have the letters MB, the L, the word for the degree here.
Dąbrowski P. 212. Year and designer unknown.