Hong Kong’s protesters have taken the unusual step of announcing a new dress code ahead of expected clashes on National Day on Tuesday: tuck your shirt in. The messages, widely circulated on social media and encrypted platforms such as Telegram, claim such a fashion choice would make it harder for undercover police to hide revolvers or batons. One officer, thought to have been undercover, fired a live round into the air in warning, during clashes in Wan Chai on Sunday afternoon. Police have not confirmed that the officer – whose face was wrapped in balaclavas similar to that of the protesters – was on an undercover mission, merely saying he fired the shot to protect the safety of his colleagues, who were “surrounded and attacked” by protesters. “You think it’s too nerdy to tuck your shirts in? It could probably save your life!” one post on Reddit-like site LIHKG read. “Everyone, tuck your shirt in on October 1 so the gun-carrying spies can be spotted.” The protesters have drawn inspiration from the “Four Heavenly Kings of Canto-pop” – Leon Lai Ming, Aaron Kwok Fu-shing, Jacky Cheung Hok-yau and Andy Lau Tak-wah – by reproducing a picture taken in the 1990s in which the four singers had all tucked their shirts in. Others called for further caution and suggested rolling up trousers too, fearing officers could hide revolvers around their ankles. You think it’s too nerdy to tuck your shirts in? It could probably save your life! Post on LIHKG National Day on October 1 – which marks the 70th anniversary of the People’s Republic of China – comes at the height of ongoing unrest in Hong Kong, which was initially triggered by a now-shelved extradition bill and then morphed into a wider movement against the government and police. Protesters have vowed to hold citywide protests, seeing it as a showdown and an opportunity to embarrass China on its prestigious day. Other measures being adopted by protesters included setting a scheduled message to reveal their name, age, ID card number and a warning they might have been arrested if they have not returned by a certain time. The protesters could cancel the scheduled message when they returned home safely. It was intended to counter the tactics of police officers, who were seen deliberately drowning out the calls from arrested protesters to nearby social workers before being taken away. On Sunday, officers were also spotted blasting sirens through loudspeakers in Causeway Bay after they arrested several protesters. Social workers who try to collect the personal details and arrange lawyers for arrested protesters had earlier criticised police, saying it was a human right for detained people to receive timely legal help.