In the rich text editor:
@K_Fabian
In a comment:
[K_Fabian](https://chowlings.com/user/K_Fabian)
For Names and Avatars:
In the rich text editor:
%K_Fabian
In a comment:
[](https://chowlings.com/user/K_Fabian) [K_Fabian](https://chowlings.com/user/K_Fabian)