Do you not know that a man is not dead while his name is still spoken?Sir Terry Pratchett, in Going Postal
In Sir Terry Pratchett's Discworld series (more about the world), "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 Going Postal, Robert Dearhear's son, John Dearheart, dies in a suspicious workplace accident while working on one of the towers, and to keep his son's memory alive, he transmits his son's name through the clacks using the message:
As long as the Clacks network existed, that message would always stay getting transmitted.
Information about the idea for the x-clacks-overhead header may be found on the Reddit-hosted discworld forum dedicated to Terry Pratchett's books, especially the Discworld series. On the Apache HTTPD, assuming the "headers" module is enabled, the header may be set with:
header set X-Clacks-Overhead "GNU Terry Pratchett"
This setup works for the Internet through headers. Aperture's web and e-mail servers include X-Clacks-Overhead headers, keeping names and memory of those who have died still alive.