For example, on WhatsApp, use the whole 25 character limit for profile name. Examples:
Bob Moved To Signal.org
Alice MovedTo Signal.org
CharlieMovedTo Signal.org
Say Signal.org, not Signal, because they won’t know it’s an app.
Use your about section too. Same on Discord, Steam, Instagram, etc.
Signal is designed to collect meta-metadata. They don’t hold any information that can tie a person to their account, but they definitely know how those accounts interact via their servers.
They know my phone number. Which in Europe is tied to me. They absolutely hold info about who talks to who