It's the question-mark box from Super Mario Brothers! Put your coins in it. Hide a mushroom or fireball (the candy of that name, obviously) in it.
The other day, I thought I'd design a 3D-printed box. This wouldn't be just any old box, but the question-mark block from Super Mario Brothers. I started to break down what would be involved in the design. I would have to come up with the base box template, then virtually punch out a grid of dots representing the correct pixels. But, I thought, if I was going to do the work to calculate a grid of pixels on the box faces, I really could just put any pattern on the side. And if I could put any pattern, I might as well turn it into a template. And if it was a template, then other people could come up with some pretty cool designs that I never even thought of.
So, if you're into the question-mark box, print the attached STL. If you'd rather have your own pattern, either hand-edit the OpenSCAD source file or build your own variant at http://netninja.com/fun/mariobox/
(Don't mind the slight wiggliness of the photo at left. I just upgraded my print head and am still optimizing the extrude settings, so many of my prints are looking a little misaligned at the moment.)