Berlin-based street artist uses QR Codes in his work, such as his Graffyard project:
I am using QR Codes to preserve graffiti for posterity by photographing the graffiti before it is removed. After the graffiti has been cleaned off by the local authorities or building owners i place a QR Code in the exact location which resolves to an image of the original. In that way a mobile phone with a QR-Code Reader can be used to travel back in time.
Here is a short video, interviewing the artist:
You can find out more about the artist’s work at his website here