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