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