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