Hong Kong CNN Business — The rare protests that spread across China over the weekend often featured demonstrators holding pieces of blank white paper, a phenomenon that has caused problems for the country’s top stationery chain. In a symbolic protest against censorship, young demonstrators held up sheets of white paper — a metaphor for the critical social media posts, news articles, and outspoken online accounts that have been wiped from the internet as thousands of people took to the streets. The unprecedented uprising, which has been largely ignored by the Chinese state media, saw demonstrators calling for an end to…