Some interesting photos of the HK protest posted on Shi Tao TV (an internet TV station?)
The Chinese on the sign doesn't just say "no," it explicitly says, "Overthrow the Communist Part." The Chinese word for "Communist Party" has three characters, the first meaning mutual, together, and so on, the second meaning property, and that last a party of faction. Notice that the mutual/together character has been crossed out, leaving only "the property party."
This photo, taken around Sept. 29, shows the scale of the protest.