“When you find this letter, I might have already been arrested or killed.”

This is how a 22-year-old protester in Hong Kong began what he worries could be the last letter to his family. He used the pseudonym “Nobody”; like most of the young people who have been confronting the police on the front lines, he fears arrest or death.

I met “Nobody” and his cohort during a recent Sunday demonstration. After 19 weeks of street battles with the police, the protesters’ roles are well rehearsed: They move swiftly, each to his or her appointed task, using codes and sign language. They assemble barricades in minutes, only to disperse in seconds.

But I came to observe handiwork of a different kind. As the violence intensified over the summer, I learned that young protesters were writing farewell notes to family and friends in the event that they were arrested or killed. They call them “Wai Shu,” or “last letters.” Some carry handwritten copies to the streets in their backpacks or wallets. Others hide them at home, in drawers and under mattresses. Several people read them to me off their phones.

“Nobody” told me he wrote his letter when he was at a protest last month in Causeway Bay, after witnessing an undercover officer fire into a crowd. “Right in front of me, live bullets,” he said. “At that moment, I learned that my life was at stake.”