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