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