http://www.gnuterrypratchett.com/

To remember a great man, his fans came up with a way to seed his memory in the internet in the same way that the fallen operators of his “Clacks” system in the Discworld books were remembered – through the use of a never logged code that flew through the system unnoticed.

In the modern version of the clacks (the internet), this has been achieved through cunning use of response headers on websites and emails. I can’t add the header to my emails yet, but every website I manage (outside of my day job) now has the header secretly being passed along unnoticed by anyone except the people looking for it with keen eyes (and cunning browser extensions).