The Masonic Cipher, also known as the Pigpen Cipher, is a geometic substitution cipher used by Freemasons to encrypt messages. It involves replacing letters with geometric shapes, fragments of a grid, often resembling tic-tac-toe or X shapes. This cipher has been used by Freemasons since the 18th century to keep their records and correspondence private. There are lots of variations.
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https://www.freemason.com/what-is-masonic-cipher/