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