Interactive poster...

Interactive poster;
Fun - Gets you involved!

I've seen a little picture of this somewhere before, but I'm glad I've found these images of it to really see how it works. I think its a really great idea although it would only be appropriate to certain audiences as you couldn't exactly send it to someone working in an office who might get their hands covered in ink without realising.
Regardless of this, as a piece of interactive design and communicating a message it works extremely well!