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