In the rich text editor:
@Username__Indeed100
In a comment:
[Username__Indeed100](https://chowlings.com/user/Username__Indeed100)
For Names and Avatars:
In the rich text editor:
%Username__Indeed100
In a comment:
[](https://chowlings.com/user/Username__Indeed100) [Username__Indeed100](https://chowlings.com/user/Username__Indeed100)