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