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