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