It took longer than I expected, but someone found the wink to Koskau Shima.
Congratulations to Kenta Tsutsui of Tokyo, who was the first to email me with the correct answer. He wins a free signed copy of the book.
(Here's a hint for all of you still looking: Check out the whiteboard on the second-to-last page.)
Now another challenge. In a Hitchcockian act of ego, I make a brief cameo appearance in The Adventures of Johnny Bunko. Another free signed copy goes to the first reader who finds it and emails me.
You're sitting in the cafe on the Lesson Two page.