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