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