In the rich text editor:
@Firewolf500
In a comment:
[Firewolf500](https://chowlings.com/user/Firewolf500)
For Names and Avatars:
In the rich text editor:
%Firewolf500
In a comment:
[![Firewolf500's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Firewolf500) [Firewolf500](https://chowlings.com/user/Firewolf500)