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