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