“Hello, world!” is a real installation for the virtual globe of
the software Google Earth. A Semacode measuring 160 x 160 meters was mown into a wheat field near the town of Ilmenau in the Land Thuringia. The code consists of 18 x 18 bright and dark squares producing decoded the phrase “Hello, world!”.
The project was realized in May 2006 and photographs were taken of it during a picture flight in the following month.

Source : Bernd Hopfengärtner (via : Geek24).