DAVID FEITH: The Number That Explains Hong Kong’s Upheaval: Off-color and packed with meaning, ‘689’ is a guide to the city’s present and future.

Invoked constantly in the streets and on social media, “689” is the protesters’ preferred nickname for Hong Kong’s leader. Both off-color and packed with political meaning, it explains why Hong Kongers are rising up—and why the government is unlikely to satisfy their demands.

At its most straightforward, the nickname refers to how Leung Chun-ying became Hong Kong’s chief executive in 2012—by winning 689 of 1,200 votes cast by a committee of local elites loyal to China’s Communist government and unaccountable to Hong Kong’s 7.2 million people. This undemocratic system is at the heart of protesters’ frustrations, so they use “689” as an insult that underscores Mr. Leung’s illegitimacy. When they chant “689, step down!” they indict Mr. Leung along with the whole Beijing-backed political structure threatening their city’s autonomy and freedoms.

A poignant coincidence makes the nickname especially potent. The number 689 evokes the Tiananmen Square massacre of June 1989, and Hong Kong—a city built by refugees fleeing Communist China’s depredations—is the world’s center of Tiananmen remembrance. This is the only part of China where it is legal to memorialize the massacre’s thousands of victims publicly. More than a million Hong Kongers rallied in solidarity with the students of Tiananmen in June 1989, as hundreds of thousands have continued to do in recent years.

You’d think that as long as Beijing loyalists were controlling elections in Hong Kong, they’d avoid vote counts that evoke the darkest episode in recent Chinese history. Yet there it is, Mr. Leung’s supposed mandate of 689 votes.

The China of June 1989 is what Hong Kong’s protesters are trying to keep at bay. They want local democracy so they can preserve their freedom of speech, freedom of assembly, rule of law and independent courts.

Hell, we’d like to preserve those things here.