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