Where this game comes from
The pigpen cipher
Freemasons used the pigpen cipher from the early 1700s. The letters sit in the cells of two grids and two crosses, and each letter is written as the shape of its cell.
One thing to hold: A gravestone: one in Trinity Churchyard, New York, from 1794, carries a message in pigpen.
Why it matters: It is easy to learn and looks like nothing at all — but anyone who knows the grid can read it.
What we don’t know: Where the cipher first came from is not known; versions of it are older than the Freemasons.