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