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