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