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