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