In the rich text editor:
@jupy314
In a comment:
[jupy314](https://chowlings.com/user/jupy314)
For Names and Avatars:
In the rich text editor:
%jupy314
In a comment:
[![jupy314's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/jupy314) [jupy314](https://chowlings.com/user/jupy314)