The masonic cipher (sometimes referred to as the pigpen cipher) is a geometric simple substitution cipher, which exchanges letters for symbols which are fragments of a grid, e.g.: img
The Craft began using it in the early 18th century to keep their records of history and rites private, and for correspondence between lodge leaders. Tombstones of Freemasons can also be found which use the system as part of the engravings.
George Washington’s army had documentation about the system; while during the Civil War, the system was used by Union prisoners in Confederate prisons.