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