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