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