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