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