signal requires a phone number to sign up. a phone number could be used to trace your signal account back to you. so why do people, especially privacy enthusiasts and experts (like edward snowden), still use it and endorse it when it lacks anonymity in that sense? i get that people could use a voip number or something to sign up, but still.
Remember, privacy and anonymity are not the same thing. Signal is an app for private communications, not anonymous communications.
You can have privacy without anonymity, and you can have anonymity without privacy, and either/both of those can be secure or insecure.