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