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