signal's servers never get your username, it's stored only on you phone so you can't be identified by signal or law enforcement. your username must be paired with a discriminator, which you're allowed to freely pick (as long as it's available). if you set "who can see my number" to nobody, your number won't be shown to anyone unless they already have your number. if you set "who can find me by number" to nobody, anyone who has your phone number in their contacts will not be able to find you unless they have your phone number
all in all, amazing implementation
