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