I saw this exact same sign in the Pearl Market in Beijing last year. The Pearl Market is a crowded multi-story "mall" where Chinese teenagers dress alike (blue Polo Oxfords are the standard) and attempt to sell 'copy watches' or Nike shoes or any other manner of pirated goods. Some of the kids ignored the 'forbidden' words and called out 'You Crazy!' to shoppers who refused to buy. However, when they said it, they smiled as if it was a game. In fact, the whole mall is 'a game.' Kids, toys, gesturing, negotiating; it is a place you have to visit, even if you don't buy. Also, watch what happens when someone warns that the Chinese police are coming. Entire showcases are shuttered in a wave of reaction, one booth after the next. Don't eat the food.