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