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