The 'OK' hand gesture that's rattled China's authorities

A video showing a Chinese girl using a clever technique to signal she needs help has been widely shared on popular social network TikTok - and is making the authorities nervous.

She is shown being escorted away by a stranger in an airport. Unable to make a cry for help, she makes a subtle hand gesture that looks like the signal for "OK".

This alerts a passerby, who immediately begins to argue with the man, and helps others recognise that the girl is being held against her will. She is then reunited with her parents.

So why has the video created such a big reaction on Chinese social media, and made the authorities so upset?

While the "OK" gesture is pretty widely understood around the world as a positive gesture, simply turning your hand so that you are facing your palm conveys a subtle message in China.

If two fingers are pressed together, your hand can look like the numbers "110" - which in China is the emergency contact number for the police.

Consequently, the video, which features actors, shows a subtle way that a child can get a message out if they are in trouble.

To push this message home, at the end of the video, a man tells viewers to "spread this gesture" so that people can signal if they are in need of help "in the event of coercion, kidnapping, or fear of your life".

The video has the appearance of a public service announcement, so many social media users assumed it had the backing of the police.

The Chengdu Economic Daily says that videos being shared on TikTok predominantly attributed the footage to the police. However, the actual origins of the video are unknown.

Today, official media are spreading the message of China's official disinformation platform Piyao, which criticises the video for being misleading, and says the police had no involvement with it.

"Such a gesture is meaningless as an alarm," it says, and argues that it might actually be counter-productive in allowing an individual to find help if they need it.

It says that it has "never publicised or promoted such an alarm method in public", and urges readers to follow the traditional method of calling the police if they need assistance or suspect someone else needs help.

Despite the authorities distancing themselves from the footage and associated advertising campaigns that have suddenly sprung up on TikTok, a huge debate has broken out online about whether the simple signal might actually be effective in helping Chinese people understand if somebody is under duress.

Some on the popular Sina Weibo microblog say that "shouting for help is more practical than gestures", and others note that the simple signal might "mislead people" and could lead to accidental interventions where none are necessary.

But in a country where tight authoritarian controls are in place and people are unable to freely speak openly, some are praising this seemingly small action to attract attention if someone's under duress.

"In fact, this kind of gesture could really be promoted for help in the country", one user says.

"As long as everyone is in agreement, we can still use it, it is still possible," another says. "As long as we're united in our understanding."

Number sequences have long proven an effective way for social media users to criticise the authorities, without immediately alerting government censors, who regularly screen platforms for sensitive words.

People have found ways to talk about the Tiananmen Square massacre of 1989 - which the government has heavily censored for three decades - by using number sequences such as "46" (4 June), "64" (June 4) or "1989".

The authorities have wised up to number sequences being used and are known for censoring many of these. But such strict censorship does mean that sometimes innocuous posts are removed by mistake.

When Taylor Swift - who is hugely popular in China - released her album 1989, the government struggled to sift posts mentioning her music from ones that might have been code for the most controversial event in China's recent history.

Cryptic number sequences and hand gestures have proven particularly effective in helping protesters in Hong Kong unite on a shared message.

Online users have been able to voice criticism of their leadership in recent years by referring to them based on the number of votes that elected them into office.

Consequently, "777" has become a nickname for Hong Kong's chief executive Carrie Lam. Her predecessor, CY Leung, was known as "689".

As protests have dominated Hong Kong in recent months, it has also become apparent that demonstrators have been able to organise themselves by communicating subtle hand signals across crowds.

Graphics showing DIY hand signals that they can use if they need supplies such as eye masks, helmets or face masks, have circulated widely on platforms like Twitter.

Which is why a small, seemingly innocuous hand gesture, going viral in mainland China and getting huge public support, would undoubtedly unsettle the authorities.

BBC Monitoring reports and analyses news from TV, radio, web and print media around the world. You can follow BBC Monitoring on Twitter and Facebook.