When I worked with Andrew, I used to write a lot of internal communications (which I am sure he loved to read). One "trick" that I used occasionally in longer emails/attachments was to put something in the text to see if people had read that far. Sometimes I made an obvious error and waited for someone to spot it. At other times I would write something like "The first person who has read this far and emails me will win a prize!".
What I didn't realise was that there is a term for such entries; they are called Mountweazels. The main reason that Mountweazels are added to text is to help spot plagiarism - i.e. a copyright trap.
There are lots of text Mountweazels but also some graphical ones too. Some street maps have rogue streets included to help with copyright control.
There are said to be many fictitious entries in various Encyclopaedias and books, including The New Columbia Encyclopedia from 1975 contains a fictitious entry on Lillian Virginia Mountweazel (1942-1973). Her biography claims she was a fountain designer and photographer, best known for Flags Up!, a collection of photographs of rural American mailboxes. It was all a lie!