User blog comment:PurplePenguin/The Grunkle Stan Mystery/@comment-67.54.173.224-20121229193139/@comment-67.54.173.224-20121231163635

Oh right! Forgot about the tattoo. Well, I think it's blueprints for the WHAT question mark wind thing on top of the Mystery Shack. It points towards some waves, and since the tattoo's blue, that's probably a body of water, like the lake. So maybe that question mark doesn't stand for the shack, but the wind thing on top.