A thing I don't like about Signal is that in principle if someone messages you by username they can't get your phone number, but the interface doesn't indicate at all. Meanwhile, if you get cold called by someone it doesn't tell you if they messaged by username or by phone number, and it's not clear by pressing "Accept" whether or not you're transmitting to them your username (if they messaged by phone#) or the phone# (if they messaged by username)… or how to prevent this.
@mcc I don't think you can prevent somebody automatically receiving your profile name if they call your number.
I poked around this part of the docs while wondering whether to push my parents over to that service.
If you have a fediverse account, you can quote this note from your own instance. Search https://chaosfem.tw/users/KatS/statuses/115577288924532457 on your instance and quote it. (Note that quoting is not supported in Mastodon.)