Comes in a variety of shapes. Here (above) we have the emblem of the Prelate in Knight Templar Freemasonry. With other symbols (below) it is part of the 6th degree of the Ancient and Accepted Scottish Rite.
Also see Samaritan by the way.
On a French 6th degree tracing board the triangles have different symbols and are conntected to Solomon and both Hirams.
Or the Knights of the Red Cross (below).
A variation of a triple triangle can be seen on a 2nd degree tracing board which can be found in Millar. I had to ‘redo’ the images, as I couldn’t make it clear enough (the original has little contrast).
Les Plus Secret Mysteres (1820) has a triple triangle placed on the Ark of the Covenant. It looks like one of the triangles above, but without symbols. About this image the book says:
The triple triangle represents the Glory of the Eternal, an emblem of the three Unities of the Trinity.
Top: Morals and Dogma, Albert Pike, (1871)
Second: General AASR jewel. Original design probably 18th century.
Third: The Book Of The Ancient And Accepted Scottish Rite (1884) Charles McClenachan
Bottom: My own redesign after a 2002 tracing board in Millar (p. 104)