I’ve been to a lot of book signings for other authors. Occasionally, you don’t ask the author to sign their book… you bring them something else.
It might be funny or an inside joke or something personal.
For example, I’ve seen Richard Dawkins sign a banana:

I’ve seen the creators of South Park (Trey Parker and Matt Stone) sign a Bible:


When I went to see theoretical physicist Lisa Randall give a talk recently, a friend had her sign a full page photograph of herself from SEED magazine. (No photos of that, but I assure you the look on Randall’s face was priceless.)
Still, I’ll admit the following is pretty inventive.
PZ Myers signing a (seemingly unconsecrated) communion wafer for a fan:
A question for all of you:
Have you ever had someone autograph something unique for you?
(Thanks to Ashley for the link!)