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