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