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