Note: The report does not explain why the number 23 becomes a taboo. But the following does.
Peter Ford, Tiananmen Anniversary Keeps Chinese Censors on Edge. Christian Science Monitor, June 4, 2012.
Quote:
"For the 23rd year in a row, the Chinese authorities today continued their efforts to impose collective amnesia about the Tiananmen Square massacre on June 4, 1989, seeking to stamp out any public reference to the event.
"As if to highlight the absurdity of how hard Sina Weibo censors were working, an impeccable and seemingly irrelevant source of information, the Shanghai Stock Exchange, suddenly turned subversive. By an extraordinary coincidence (or maybe not), the Shanghai Composite Index, which measures the market’s daily movement, fell on Monday [June 4] by 64.89 points, in an uncensorable reminder of the date of the massacre.