A Lead

... In 1795 George Murray invented a version that is close to the system currently used in Discworld: a set of six shutters that could be opened or closed, thus giving 64 'codes', more than enough for the entire alphabet, numbers 0 to 10 and some 'special' codes. The system was further developed but ceased to be cutting-edge technology when the electric telegraph heralded the wired age. The Discworld semaphore (or 'clacks') has been taken much further, with mighty trunk route towers carrying bank after bank of shutters, aided by lamps after dark, and streaming messages bi-directionally across the continent.

The Science of Discworld II: The Globe (pg. 181)

1:11 pm
VICTORY IS MINE! AAHAHAHAHAHAAA!! Thank you library! Thank you random website that popped up in my search! Thank you Geoffrey Wilson!

HAH! HA HA HA! HA HAAA!

( And within... )