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