I would imagine that the issue that people have here isn't so much that you can hide from other users, but whether or not you can hide your information from the company behind Signal. I'd assume that if you can't hide from the company, then you can't hide from the US government. We know that you can extract messages from a compromised phone because they aren't encrypted at rest. Which I guess would mean that even if you have disappearing messages and similar, your messages could proably still be extracted from a group chat with a comprimised user in it.

If we go full tinfoil, then do you really trust Apple and Google to keep your Signal keys on your device safe from the US government?

It's probably not that bad, but I do know that we're having some serious discussions on Signal here in Europe because it's not necessarily the secure platform we used to think it was. Then again, our main issue is probably that we don't have a secure phone platform with a way to securely certify applications (speaking from a national safety, not personal privacy point of view).