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