What are they smoking in there? Just straight weed, or are they mixing it with tobacco to create a British-style spliff, or what? I wonder if their pot is spicy.
But seriously: this is a word challenge as well, of course, as a cultural one. "Rolling" can be a verb, thus the humor of this sign. But "rolling" can also be an adjective, which I'm sure means something different in Chinese--bad translation!