Where's the CTA

The other I day I came across one of my favorite books, full of humor, mystery and action and loaded with pages of content. The Where's Waldo book series is truly one of a kind... so it occurred to me... What would Where's Waldo look like in this digital world? And to take it a step further? What would happen if the website was such an immersive experience it challenged you to find the CTA to sign up?