This piece is linked to a Bitcoin account through the QR code, making it a paper wallet. It currently has (as of 2013) 0.1BTC, around 100$ in Bitcoins loaded onto it, and is enjoying the view of the city and the city possibly the view of it.
Anybody can add Bitcoin to the wallet, but only the keyholder can take it out.
Update 2019: After further growth, the maximum this wallet was worth so far was 2000$ in 2017. The 0.1BTC are still linked to this painting and have not been touched.
Update 2021: The new maximum has been 6000$.