Schulz and de Vienne, the authors of Nelson Barbour: The Millennium's Forgotten Prophet, on their private history blog have a long write up that is destined to be an appendix in their next book. I'm breaking rules by quoting it here, but then I've never been good at obeying all the rules:
A pyramid shaped monument was installed in the Bible Student cemetery in Pittsburgh. The cemetery is occasionally described as Masonic. It’s not. There is a Masonic temple nearby built years later. There is no connection. The pyramid was intended as a general monument with the names of those buried in the Watch Tower plots engraved onto open books. Rather than being a Masonic symbol, the open book motif derives from the book of Revelation. Those who want to cast Russell as part of some great Masonic conspiracy claim the pyramid embodies the “all seeing eye.” It does not. The pyramid symbol refers to Russell’s belief, shared by many others who did not otherwise hold his views, that the Great Pyramid at Gizah was a divinely inspired testimony in stone to Bible truth. We trace the development of this idea in Chapter Three. The use of the pyramid as a monument was suggested not by the back of the US dollar which had an entirely different design in 1920, but by the grave marker for Charles Piazzi Smyth, a prominent pyramidologist and Astronomer Royal of Scotland.
The monument was installed in 1919, some years after Russell’s death. One source suggests Russell designed it, a Bible Student convention report saying: “The Pyramid, as you will note, has an open book carved on each side, intended by Brother Russell for the names of Bethel workers as they ceased their work and were laid at rest, awaiting the great Resurrection of the first-fruits of the Lord.” [1] A Bible Student web page takes pains to blame the pyramid monument on Rutherford rather than Russell. Neither of these statements is correct. The monument was designed not as a memorial to Russell but “as a memorial to the society.” It was “designed by Brother Bohnet, and accepted by Brother Russell as the most fitting emblem for an enduring monument on the Society’s burial space.” According to Bohnet, work started in 1914. The pyramid’s purpose was not Masonic. [2]
[1] Souvenir Notes from the Reunion Convention of Christian Bible Students: Pittsburgh, Pa., November 1-2-3, 1929.
[2] Souvenir Notes from the Bible Student’s Convention: Pittsburgh, Pa., January 2-5, 1919, page 7.