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