In the rich text editor:
@Duck
In a comment:
[Duck](https://chowlings.com/user/Duck)
For Names and Avatars:
In the rich text editor:
%Duck
In a comment:
[![Duck's Avatar](https://chowlings.com/images/avatars/1600.png?v=1659717767)](https://chowlings.com/user/Duck) [Duck](https://chowlings.com/user/Duck)