In the rich text editor:
@28cats
In a comment:
[28cats](https://chowlings.com/user/28cats)
For Names and Avatars:
In the rich text editor:
%28cats
In a comment:
[![28cats's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/28cats) [28cats](https://chowlings.com/user/28cats)