You can now hide you phone number, according to the blog post.
[...] Selecting “Nobody” means that if someone enters your phone number on Signal, they will not be able to message or call you, or even see that you’re on Signal. And anyone you’re chatting with on Signal will not see your phone number as part of your Profile Details page – this is true even if your number is saved in their phone’s contacts. Keep in mind that selecting “Nobody” can make it harder for people to find you on Signal.
[...] Selecting “Nobody” means that if someone enters your phone number on Signal, they will not be able to message or call you, or even see that you’re on Signal. And anyone you’re chatting with on Signal will not see your phone number as part of your Profile Details page – this is true even if your number is saved in their phone’s contacts. Keep in mind that selecting “Nobody” can make it harder for people to find you on Signal.