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