Dearest 100 Hour Board,
A while back I remember learning that the song Another Postcard by Barenaked Ladies was written because the lead sing had, in fact, been receiving chimpanzee postcards. Did we ever find out who was sending the postcards and why chimps were the focus?
To answer your question, I couldn't find any reputable sources suggesting the postcards were anonymous.
A *slightly* more authoritative source (Wikipedia... does that count?) as well as Genius Lyrics say the song was actually inspired by a neighbor sending one of Page's children a single postcard with a chimpanzee on it.
The Genius Lyrics are fun because someone added pictures for every example of a chimp postcard in the song. See here