They used hand signals.
A 2019 Reuters article by Marco Hernandez and Simon Carr (“Coordinating chaos: The tactics protesters use to fortify the frontlines”) reports on how the hundreds of thousands of Hong Kong residents who packed the streets for months in protest against the Chinese government organized delivery of supplies to parts of the crowds.
There were hand signals for helmets, umbrellas, masks, plastic wrap, goggles, water, asthma inhalers, barricades, cable ties, scissors, and Allen keys, and another signal to indicate that requested supplies had arrived.
Protesters have adopted hand signals to communicate across a large and loud crowd of people. When supplies or equipment are needed in a specific area, large groups have been seen signaling to those further away to bring or pass items….
Protesters use whatever items they can to slow the advance of police or stand their ground, including stacks of metal barriers, bins and building materials…. Umbrellas can protect against some of these police tactics by maintaining distance or acting as a shield.
Police have regularly fired tear gas and pepper spray at protesters. Demonstrators often use equipment such as goggles and gas masks or face masks to protect themselves. Cling film has also been used to protect the skin from the burning sensation of tear gas.
Because of the repressive measures enacted since 2019, the kinds of measures that the protestors had tried to prevent, it doesn’t seem that Hong Kong residents will be able to stage similar demonstrations anytime soon. The current China-installed government of Hong Kong has many ways of keeping such protests from even getting started. But circumstances change. Information on tactics of protest may come in handy again one day.