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