Walking in the street today I saw this sign in a park in Hong Kong.
It might seem a bit strange to you, but there is some foundation for this. In China, spitting is normal, extended and generally accepted; at least in all three cities I have been before, and I do know than in many others too.
Hong Kong is really close to mainland China, and in fact, it is part of China, but they still have many english ways of living, and one of them is that spitting is not something socially accepted, as in the rest of the country, so they have set up local penalties to fight against that.