Technically, anything is copyrighted the second it is created.

I created the current 3D coin graphic.  And I would not really appreciate someone selling shirts of it.
Though I don't mind people using it virtually/on-line for an icon or website. That's what it's for.
But selling completely for it's "graphic value", like on a t-shirt, would bug me.

You'd have to ask Evan or somebody official about the D logo itself.
Evan and/or Darkcoin Foundation own that. It was contracted and paid for thru DesignCrowd.

I was thinking of doing some shirts with it myself since I have a nice super hi-res version and can make variations.
But I haven't heard anything back from a similar inquiry (about t-shirts) to Evan.