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