In the rich text editor:
@crestfallen
In a comment:
[crestfallen](https://www.whistlercrest.com/user/crestfallen)
For Names and Avatars:
In the rich text editor:
%crestfallen
In a comment:
[](https://www.whistlercrest.com/user/crestfallen) [crestfallen](https://www.whistlercrest.com/user/crestfallen)