"@dang" doesn't do anything last I heard (though at this point it's used often enough that maybe the HN folks should consider it). If you want to reach the mods you can contact hn@ycombinator.com I believe.
I did.
What is a black ribbon?
Probably meant black HN top bar.
An HN website tweak as a sign of respect on the passing of notable contributors to the tech world: