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