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