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