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