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