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