Semaphore

While some secret languages are hidden and stealthy, semaphore
is grand in its expressiveness

A nautical semaphore flag.

Devised in 1794 by Claude Chappe, semaphore originally involved large towers displaying messages that could be seen by a network of telescopes winding its way throughout the French countryside. While revolution weakened the nation's defenses, semaphore preserved France's ability to communicate mysteriously, their tactical messages hidden in plain sight from their potential enemies.

In subsequent centuries, the maritime community adopted semaphore and translated the language into a series of flag positions. These positions represent the letters of the alphabet, as shown below: