SHANGHAI — If you were driving in China recently, you might have gotten in trouble had you tried honking your car horn like this:
The pattern is a secret code of sorts for loyal users of two Chinese social media apps to identify themselves. Honk the signal while idling at a red light, and if you hear it in response, then you know a fellow fan is near.
This week, though, China’s top media regulator closed one of those apps. Officially, the app, Neihan Duanzi, was shut down for hosting “vulgar” jokes and videos. But it and another app, Douyin, which helps users make goofy music videos, have brought together legions of fans who make themselves known to one another in the real world.
That has led some to wonder whether the platform’s tight-knit user community, with its own subculture and obscure vocabulary, had angered the authorities. China’s ruling Communist Party has a history of cracking down on groups that seek to organize citizens outside its sphere of control.
Users of both apps put decals with the apps’ names on their car windows. They hold meet-ups where they chant invented slogans — “Sky king covers earth tiger, stewed chicken with mushrooms!” one goes — and do things like arrange their cars to spell out the name of their city.
They also honk rhythmically at crowded intersections, prompting rebukes from the police in several Chinese cities recently.
No ideology appears to link the apps’ fans, although their online videos suggest that sports cars and community service are common enthusiasms.
In one clip, a column of cars parades down an empty highway, headlights flashing.
In another, a bronze sports car drifts and does doughnuts at an abandoned intersection.
One popular Chinese variety show earlier this year also chronicled some the good acts done by the fans. In China’s sparsely populated west, one group pitched in to help the elderly and entertain children. On Chinese social media, enthusiasts from other parts of the country posted photos after donating blood and sending secondhand goods to remote schools.
China has undergone dizzying social change over the past decades. The internet has become a place for many people to seek out personal connections and community.
“I’m truly sad. My friend and I both cried while talking about it,” Liu Wei, 23, an aspiring R&B composer in Shanghai, said of Duanzi’s closing. He had been a user of the app for more than five years.
“So many years of love,” Mr. Liu said. “It’s like I lost a brother.”
Bytedance, the company behind both Duanzi and Douyin, has become one of the most highly valued technology start-ups in the world. But it has to manage the material on its platforms carefully in order to stay on the right side of China’s censors. Two more of the company’s popular platforms have been pulled from app stores in the past week.
Zhang Yiming, Bytedance’s founder and chief executive, apologized in a statement for failing to adequately police content, and for the company’s failure to respect “core socialist values.”
“As a start-up developing rapidly in the wake of the 18th National Congress, we understand deeply that our rapid development was an opportunity afforded to us by this great era,” Mr. Zhang wrote, referring to the 2012 Communist Party confab at which President Xi Jinping took office.
“I thank this era,” Mr. Zhang wrote. “I thank the historic opportunity of China’s economic reform and opening-up. I thank the support the government has given to the technology industry’s development.”
China’s highest media regulator, the State Administration of Radio and Television, did not respond to a faxed request for comment about why Duanzi was shut down.
But in recent days, the authorities in China have instructed news outlets to suppress information about fan gatherings, according to censorship orders reviewed by The New York Times. Any mention of “revolt” in connection with Duanzi fans has been ordered scrubbed. Outlets have also been told to censor photos, videos and articles attacking the media regulator or calling for protests.
“It’s almost like there’s a war on humor and fun,” said Joshua Rosenzweig, a Hong Kong-based adviser at Amnesty International. “And the only things that are allowed are the things that fit into the official propaganda messages: the ‘China Dream,’ the ‘Belt and Road.’ It has to be connected to what the party wants people to be concerned about.”
Internet crackdowns are nothing new in China. But the latest seems more specifically aimed at making sure there is not too much online that might vie with the government’s messaging for people’s attention, Mr. Rosenzweig said.
“They want to do more, I think, to proactively shape people’s thinking through the media,” he said, “and they can’t have this kind of competition.”