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