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