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