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