Thanks to some Redditors. For those who are not familiar with the Clacks and/or the Discworld Industrial Revolution novels, the Clacks are semaphore towers sett across the countryside of the Disc, which relay messages, sort of akin to a telegraph. Very slight spoiler for Going Postal ahead.
In Going Postal, the names of dead Clacksmen are kept alive forever by passing them between the towers with the code GNU in front of the name.
Folks over at Reddit have come up with code to embed Sir Terry's name with the GNU code into various websites, and apps.
A utterly fitting tribute.