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