https://web.archive.org/web/20241117122125/https://support.signal.org/hc/en-us/articles/6829998083994-Phone-Number-Privacy-and-Usernames-Deeper-Dive#:~:text=A%20username%20is%20a%20way,are%20chatting%20with%20in%20Signal

Signal allows you to set usernames. They are unique but temporary (and you can have only 1 at a time). User names can be used to connect to you without sharing your phone number. Set an optional username in Settings Profile. They have two numbers at the end (you can set them).

User names can be shared in three ways: - tell someone (and then change it so they cannot communicate it further) - share a QR code - share a unique URL (which does not contain your username in clear text)

Signal can't 'easily' see which phone number has which username. But given a username it can find the associated phonenumber. 'easily' means it can be done though, and thus both ways.

An old username will become available to others after a week, meaning imo they should not contain any identifiable or associative information.

Found this through someone suggesting that sharing your Signal username through Mastodon would allow private msgs. Yes, but the world will know your username, so you're open to all people who might think it fun to msg you.

https://support.discord.com/hc/en-us/articles/12620128861463

Having multiple names is an interesting manifestation of having multiple identities. Do you tend to use your "real" name, a consistent username across services, or different usernames based on the kind of service? What happens when those contexts collapse (like when you give a work acquaintance your personal email address).