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