SHANGHAI — If you were driving in China recently, you might have gotten in trouble had you tried honking your car horn like this:

Beep.

(Pause.)

Beep, beep.

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 tightknit 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 the name of their city.