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