1: Right click on the GNOME panel;
2: Click "Properties" in the context menu.
You will see a joke message with the picture of a strange animal (cow or gnu??) with 5 legs and the text that includes the Knighters who say "NI!" as developers of the program, and more!
Tested only on GNOME 1.4, but should work on recent versions. (www.gnome.org)