Ah ok now I get what you mean. Hashing for phone numbers is ineffective so it’s a two way lookup. Is the population using Signal small enough that this doesn’t just equate to surveiling everybody?

The question is: What privacy do I loose by signing up to Signal with a phone number instead of hypothetically a username.

If you are being monitored, they know your phone number. With that they know you are using Signal, but nothing more. Messaging through Signal is safe.

If you are not being monitored, nobody knows you are using Signal. Messaging through Signal is safe

I still don’t get it. What is bad about signing up with your phone number? All readable Info that governments can force out of Signal is. “Yep this guy uses Signal, signed up last year” so nothing is lost (except if they use that as a sign you are a terrorist, but then they just wanted to monitor you anyway in the first place)

What about standard