You chose your username here and in most other places.
You can even change it easily on many platforms.
Your username doesn't require you to show your ID and have your calls tapped and traced towards your person.
The problem I'm seeing here with the responses is that people are only thinking of "one move." That first move is creating a anonymous username. Yay. Easy. Now here's the problem. How do I share that while staying anonymous? What conditions do I need? If I can only have one username for all of Signal, does that create a bigger problem? There's a few more "moves" for you and these are what I'm looking for answers to.
Do you want me to continue?