http://www.diamondcomics.com/(has an overlaid silhouette of scary hands and rats)
In today's Diamond Previews, it lists the special edition of Coraline having a run of 4000 copies (as opposed to the 500 run you mentioned on the March 15th Journal)
(They relist all of your novels, and list a neilgaiman.com/coraline whch doesn't see to be up yet)
The Diamond-only edition, with the 16 extra pages (notebook pages, a little explanatory text, variants of Dave McKean illustrations, etc) will be limited to 4000 copies. Of these 4000, 500 copies (or less) are going to be signed and limited. I'm not entirely certain what the conditions are for retailers and customers being able to get either one of the 4000 or one of the 500. You'd think I'd know, but, other than knowing it's a backlist promotion, I don't.
The cover that Diamond reproduces is essentially the same cover as the one I put up here -- the main difference is the typeface and layout, which is correct on the one that I posted here on the journal.
The silhouettes of rats and hands and such will, on the finished book, be done with a glossy, reflective overlay (except on the Diamond limited edition, where it will apparently glow in the dark).