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