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