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