In the rich text editor:
@Ethan1005
In a comment:
[Ethan1005](https://chowlings.com/user/Ethan1005)
For Names and Avatars:
In the rich text editor:
%Ethan1005
In a comment:
[![Ethan1005's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Ethan1005) [Ethan1005](https://chowlings.com/user/Ethan1005)