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