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