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