Fun-A-Day idea #10:

Make an educational plaque.

Courtesy of the Learning to Love you More project: "Come up with some simple but useful information that can be made into a plaque or sign and then install it in some public place for people to learn from and use.  [...]  Note: do not bother making a plaque that is witty. Think of information that you routinely wish you had, and provide it to the public.