In the rich text editor:
@Codeine
In a comment:
[Codeine](https://chowlings.com/user/Codeine)
For Names and Avatars:
In the rich text editor:
%Codeine
In a comment:
[![Codeine's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Codeine) [Codeine](https://chowlings.com/user/Codeine)