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:
[](https://chowlings.com/user/AvacardO) [AvacardO](https://chowlings.com/user/AvacardO)