I once came across some code, written by a coworker, that consisted of deeply nested blocks. I added a comment that simply contained a URL:

  // http://photos3.meetupstatic.com/photos/event/4/b/c/2/600_436939394.jpeg

I don't know if anyone ever noticed this comment and followed the URL, but I hope they did and were amused. (The code was eventually refactored/rewritten, so the comment no longer exists in the codebase.)