If a game is not made, someone could simply make a quick website that sells stamps (like for ink pads). The stamp will say something like "Bitcoin is Happening" and it'd be small so it'd fit in the margin border of the bill. Anyone interested in promoting this viral phenomenon can order a stamp and join the legion.
But this change everything about the idea.
The all game must be free and easy to do.
Ordering stamps, paying for it, putting on the banknote ... it doesn't work on this way :\