There’s no such social graph to speak of. Signal does not know who is speaking to whom.
The only people who know this are people operating the server. Period.
Three-letter agencies have served them legal subpoenas many many times and they never turn over anything more than the above information.
See the link I provided above.
Filter for…what, exactly? The hundreds of millions of people who value private and secure communications?
Yup, that's precisely what it's a filter for.
We do, because they publish them publicly.
Trust me bro is not a viable model for anybody who actually gives a shit about their privacy.
The reality of the situation is that Signal asks users for information it has no business collecting during the sign up process, and this information can be used in adversarial ways against the users. People using Signal are making a faith based judgment to trust the operators of this server.