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