Signal & WhatsApp are not secure enough. Meta/Facebook regularly give data & metatadata to the cops & Signal is centralized & not self-hosted by your crew so while messages are encrypted, the metadata still isn’t. If you must use Signal, I would pick Molly as an Android client since you can a) encrypt the messages under a separate password for storage on seizure & b) you can use the UnifiedPush version to make sure your notification metadata isn’t going thru Google’s Firebase servers. Protests are the ideal place for Briar as it is works via mesh net so internet & SIM cards are not required (but years ago wden I tried it, the app was a major battery drainer).