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