X-Clacks-Overhead
About the Signal X-Clacks-Overhead is a non-standardised HTTP header based upon the fictional work of the late, great, Sir Terry Pratchett. In Terry Pratchett's science-fantasy Discworld series, "The Clacks" is a network infrastructure of Semaphore Towers, that operate in a similar fashion to telegraph - named "Clacks" because of the clicking sound the system makes as signals send. In Sir Terry's novel "Going Postal", the story explains that the inventor of the Clacks - a man named Robert Dea