A reader in Washington, D.C. was reading a political thriller set in D.C. In one scene, a character leaves a foil-lined envelope in a niche in a statue in a D.C. traffic circle. The reader recognized the statue, and thought Wouldn't it be cool if there really was that niche in that statue? So he decided to find out.
He went to the circle, searched the statue based on the description in the book, and found...a niche. With an envelope. He opened it. It was foil-lined. And inside the envelope in the niche in the statue in the circle was this note:
"Wasn't that a good book?"