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