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