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