GNU in Discworld (Going Postal, The Clacks coding)
“G” means that the message must be passed on, “N” means “not logged”, and “U” means the message should be turned around at the end of a line. (This was also a realworld tech joke: GNU is a free operating system, and its name stands, with recursive geek humour, for “GNU’s not Unix”.) The code causes [the person's name] to be repeated indefinitely throughout the system, because: “A man is not dead while his name is still spoken.”

GNU Gary Owens (aka Gnu)