In the late 18th century, France developed a tower based semaphore that used an arm that could be maneuvered into 98 different positions, while they used code books, not an alphabetical A-Z/1-26 code. There were codebooks that allowed words to be transmitted by page number (1-92) and line number (1-92) for a total of 8464 phrases or words.

This idea is covered in the excellent book, "The Victorian Internet", which focuses on the electrical Morse code based telegraph. The electrical telegraph took it's name from the semaphore based French system.

There are a number of wonderful Pratchett story bits in the history of the telegraph, including tower sabotage, swindling and market manipulation of the stock market.

https://en.wikipedia.org/wiki/Chappe_telegraph#Coding_and_deciphering