Duane used his handy phone to come up with the answer to the question, what do you call it when those sailors talk to each other with flags. Below are the letters A and B
Semaphore telegraph, optical telegraph, shutter telegraph are all names used to describe the passing of information visually. The lights, with shutters that are open and shut in a specific sequence, are also called semaphore telegraph.
In 1792, France set up a network of 556 optical telegraph stations stretching almost 3,000 miles. It used large movable wooden boards and was used for military and national communications until the 1850s.
Semaphore is still used today at sea and is acceptable for emergency communication in daylight or using lighted wands instead of flags, at night.
'Telegraph Hill' in San Francisco is named after the semaphore telegraph which was established there in 1849 to signal the arrival of ships into San Francisco Bay.