A mysterious man called the Shadow was a popular serial hero in the 1930s.

The story “Chain of the Code” contained a so-called “directional code”. In addition to the characters for the 26 letters of the alphabet and a space, there were four other symbols 1 – 4. The lines represent directional arrows and indicate in which direction the leaf with the message should be held:

• Symbol 1: The sheet is held normally
• Symbol 2: The sheet is turned 90 degrees to the right
• Symbol 3: The sheet is rotated 90 degrees to the left
• Symbol 4: The sheet is rotated 180 degrees

The extra symbols can be written at any time, making frequency analysis more difficult.