It was a common practice in Zen Buddhism to write down one's insights in verse form on scraps of paper or pieces of bamboo, and hang them on walls or trees, often anonymously. Nowadays this has become a formalized tradition in Japan, and takes place at cherry blossum time.
This collection of graffiti was inspired by the great Zen masters. Perhaps the most famous Zen graffiti of all was the sixth Patriarch`s verse which was written on a monastery corridor wall: "There is no bodhi tree, nor stand of mirror bright, since all is void, where can the dust alight?".