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