Pigpen Cipher

Two hash grids and two X grids hold 26 letters between them.

1. Draw a 3×3 hash grid and fill A-I into its cells.
2. Draw a second hash grid, fill J-R, and put a dot in each cell.
3. Draw two X shapes and fill S-V and W-Z, dotting the second.

Encipher by drawing each letter's surrounding lines.

1. Write a sentence, converting each letter to its cell shape.
2. Hand it to someone with the grids and have them read it back.
3. Now time yourself writing a second message.

Compare its statistical behaviour with a letter substitution.

1. Encipher a long passage and tally how often each SYMBOL appears.
2. Chart it against your English reference profile.

The grid arrangement can itself carry a secret.

1. Fill the grids with a scrambled alphabet rather than A-Z in order.
2. Or reorder which grid is dotted.
3. Exchange messages with a partner using an agreed variant.

Geometric substitution alphabets of this kind are old — versions are associated with the Knights Templar and with Jewish and Rosicrucian traditions — but the well-documented use is Freemasonry from the eighteenth century, for records and correspondence. It is common on Masonic gravestones, and Union prisoners used it during the American Civil War.

Its niche is a real one. Pigpen is fast to write, needs no equipment, can be reconstructed from memory, and is visually distinctive — which suits a fraternal record or a monument, where the goal is discretion and identity rather than resistance to a determined analyst. Judged as a secrecy system it is modest; judged against what it was actually used for it is well fitted.

The variants are the interesting part for a catalogue. Which letters go in which grid, whether dots or bars mark the second set, and whether the alphabet is scrambled all vary between traditions — so a surviving inscription can sometimes be attributed to a particular lodge or period by its layout alone. The differences are historical evidence, not errors.

It has become a teaching cipher, appearing in puzzle books and games precisely because the rule is discoverable. Solving it without being told is often a person's first experience of cryptanalysis, which is a decent argument for its continued place.