As far as I know the crypto has been pretty thoroughly peer-reviewed and there is source code available for the app + crypto implementation. If I recall it did associate my account with my phone number at sign-up. I've seen Antifa fags using Signal and their middle and upper management tends to be pretty tech savvy as they are composed of mostly middle management from various tech companies. I've been looking at Wire also because my understanding is that is another implementation of the same crypto used by Signal. Wire also DID NOT require a phone number when I signed up. That said, you should assume that any Internet-based comms is not completely trustworthy. 1) Best way to defeat crypto is with a rubber hose. 2) It's entirely possible alphabet agencies have quantum tech that can defeat what is currently the best crypto available to private citizens. 3) Side-channel attacks abound.