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