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