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