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