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