" if the ___ has your unlocked phone they can read your signal messages. "
It's worth noting you can add an additional security check pin/bio/pass to signal that is different from your phone unlock.
The protester had also uninstalled signal from phone (even with access to the phone, they would not have access to signal, if they had reinstalled signal, and some how got the security pin or passphrase, they wouldn't be able to load the prior messages, without either, no messages at all).