The sources said the core figures had been taught how to use face masks, helmets, gloves and goggles to hide their identities, how to daub surveillance cameras with paint and to use hand signals for on-site communication, making it difficult for local police to trace them and gather evidence.As well as being used to protect protesters from pepper spray, umbrellas served to build barriers to prevent officers from filming them in the act, according to the source.
“After attacking police cordon lines, those hard-core protesters normally retreat and use the umbrella-wall as a screen to change their clothes and then leave the scene to avoid being identified by police,” he said.
[...]
One group comprised 200 to 300 hard core radical protesters. “They are called martyrs and are deployed on the front line. They provoke police on site and use force and violent acts to attack police cordon lines and fight with officers,” another source said. After the attack, they retreat and change their clothes and leave before others move in.
https://www.scmp.com/news/hong-kong/politics/article/3019445/police-looking-more-700-core-extradition-bill-protesters
