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