Berlin-based artist Sweza has managed to make QR codes interesting in his "Graffyard" project. He photographs graffiti before it is removed by local authorities. Once removed, he places a QR code where the graffiti was, which links to an image of the original artwork when viewed through a reader.

 
 
My only comment is that it would be great to be able to view this sort of thing in real time in an augmented reality viewer...It seems to require a "scanning" stage in order to reveal the hidden information.