QR codes on buildings and in fields

Those that know me well, know that I am big fan of QR codes and how they can enable the mobile internet.

Scenario: a camera-phone takes a photo of the 2D bar code (as above) and the phone decodes it and launches a browser at the web page that is encoded in the bar code. (Very big in Japan.) Mobile discovery made easy, n'est-ce pas?

Anyway this article, claims that the largest QR code ever created is 10 metre square one that was projected onto a building in Ginza, Roppongi Hills and Shinjuku (ie Central Tokyo) for Northwest Airlines.

This got me thinking about large QR Codes.

• A QR code created by selectively turning on and off the lights in a building to create the code (An organisational nightmare, I admit!).
  
• A QR code made by ploughing a field. (Similar to crop circles and ploughing pictures).
  

Any others, people?? Cars or humans in a car park?