I was about to comment similarly that this is totally a wireless telegram system!
For anyone who doesn't want to click the link, it's a visual telegram system similar to semaphore codes, or the 'clacks' in Terry Pratchett's Discworld novels.
And, as every communications systems, it was abused (as mentioned briefly in the WP page) by stock brockers between Paris and Bordeaux via a side channel attack.
They used it to covertly transmit swing in trading prices between the Paris stock exchange and Bordeaux. If memory serves, they used unused symbols or abused error correction, I don't remember which, but from a technical standpoint it was pretty advanced and covert.
I seem to remember they only got caught because somebody snitched them when they suddenly got veeeery good a predicting prices in Bordeaux, some 400km away from Paris.
It appears transmission speed for a symbol was on the order of magnitude of 7 meters per second, and full messages travelled 400km in 9 minutes instead of 4 days by horse.
So speed was a ginormous improvement despite low bandwidth and very high capex & opex and limited operating hours.
It operated from 1793 to 1854 in continental France.
For anyone who doesn't want to click the link, it's a visual telegram system similar to semaphore codes, or the 'clacks' in Terry Pratchett's Discworld novels.