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