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