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