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