Since 1990, Post Alley (below Pike Place) in Seattle has been filled with impatient young people waiting in line for tickets (presumably concert tickets), sticking broken gum to the wall and attaching a coin, which then falls off or is removed. It leaves a round mark. More and more gum spread like a "permit" posted on telephone poles in the streets of China, until 1999, the authorities decided to give up cleaning the gum on the wall of the alley, so the gum street wall slowly became a local landmark tourist attraction, and more and more people added countless bacteria and color to the place.