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