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