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