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