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