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