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