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