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