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