The pigpen cipher is a substitution cipher that swaps letters with simple symbols made of straight lines and dots. Its use dates back to the 1700s. Though encoded messages bear no resemblance to English, the pigpen cipher is easy to understand and decode.
The pigpen cipher uses a grid of nine squares, similar to a tic-tac-toe board, and an X. These shapes are written twice: the first one is blank, and the second one contains a dot at the inner corner. The letters of the alphabet are then written into the empty spaces. The traditional pigpen cipher key places A through I in the first grid, J through R in the dotted grid, S through V in the blank X and the remaining letters in the dotted X. Users may map the letters differently to add an extra level of security.