This article originally appeared on ABACUS Chinese internet users have many ways to refer to June 4, 1989. Some call it May 35th. Some write 6489 or 8964. Others turn to mathematical equations to refer to those number sequences: 32x2, 88+1, 65-1, 2^6. All of these terms are diligently censored on China’s internet. They are just some of the more than 3,400 expressions used to refer to the bloody government crackdown that happened that day, quashing student protests that began in Beijing’s Tiananmen Square and left hundreds, possibly more than 1,000, dead. But the effort to obliterate the event from China’s collective memory doesn’t stop there. Pictures, expressions and anything else that could potentially remind people of the event can disappear from social media platforms such as WeChat and Weibo in a matter of seconds. Some examples of the random of words already censored are “that day,” “ Pelosi ” and “candle.” A somewhat extreme example is not being able to send RMB 89.64 or RMB 64.89 through WeChat Pay. To avoid censorship, savvy online users have been disguising the event in memes. Instead of putting up real photos from the protests, they concoct their own, with many referencing the famous Tank Man -- including one famous meme that replaces the tanks with rubber ducks. How Weibo became China’s most popular blogging platform Weiboscope, a project led by Hong Kong University’s Journalism and Media Studies Centre, holds a trove of images deleted from Weibo and later publishes them on Instagram and Pinterest. Some of these are pretty creative. As users have become more creative in posting visuals, the censors have also kept up. Much of the censorship is automated now. Some posts might not even get published. China’s most popular messaging app, WeChat, can filter both text and images , according to findings from CitizenLab. However, machines can’t get everything. Dr. Fu King-wa, an HKU associate professor working on Weiboscope, believes some of the censoring still has to be done manually because it requires knowledge of key events and well-known scenes from 1989 to spot photos with a message that might not seem objectionable at first sight. WeChat, the app that does everything The censors’ efforts, however, have made users turn to more obscure references. A black square, a string of characters that vaguely resembles a man and a tank, or even a 404 error message can be used to point to June 4th. The Chinese government is intent on deleting the event in other ways, too. Around this time of year, websites regularly announce “maintenance” and place restrictions on their platforms. WeChat stops Chinese accounts from being able to change profile pics, and this year, streaming sites such as Bilibili halted real-time bullet comments that fly over videos. Previous efforts to mark the date have also gotten Foursquare blocked , likely because it was used to organize check-ins at Tiananmen Square. It’s a cat-and-mouse game between censors and online voices of dissent. The event has been erased from public consciousness to such an extent that the memes might not even make sense to many people even if the censors let some slip by. The admin of a Facebook page dedicated to posting Tiananmen memes is just one of the people determined to not let June 4 be forgotten. The admin, who only gave his name as Kevin, was inspired when he found that his Chinese friend did not know what happened on that day. “Memes are truly the next gen’s method of communication,” he said. “With my connection with the youth (as I am young too), I want to reach out [with] the message of truth [to] where it has long been distorted.” For more insights into China tech, sign up for our tech newsletters , subscribe to our Inside China Tech podcast , and download the comprehensive 2019 China Internet Report . Also roam China Tech City , an award-winning interactive digital map at our sister site Abacus .