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