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