Semaphore

I love a new-to-me word. Recently, it was semaphore. 

Around New Year’s Eve, I was telling a colleague about the time I was living in downtown Vancouver, in a high-rise, and on New Year’s morning I saw a woman’s long, elegant evening gown flapping in the wind, perhaps thrown aside near the window in the wee hours, where it slipped out, and then caught. It was the old BC Hydro building, so there were no balconies, so I don’t even think they knew it was there. I always imagined the confusion and mystery they ensued.

My colleague said, perhaps it was a signal known to few... perhaps it was a semaphore.

Courtesy of Britannica: 

Semaphore, method of visual signaling, usually by means of flags or lights. Before the invention of the telegraph, semaphore signaling from high towers was used to transmit messages between distant points. One such system was developed by Claude Chappe in France in 1794, employing a set of arms that pivoted on a post; the arms were mounted on towers spaced 5 to 10 miles (8 to 16 km) apart. Messages were read by telescopic sightings. Modern semaphores included movable arms or rows of lights simulating arms, displayed from towers and used to signal railroad trains. Semaphore signaling between ships, now largely abandoned, was accomplished by persons who held a small flag in each hand and, with arms extended, moved them to different angles to indicate letters of the alphabet or numbers.