FrostyTech posted a review on the Xigmatek Dark Knight SD1283 Night Hawk Ed. Ceramic Coated Heatsink

Remember that F-117 'Nighthawk' aircraft shot down over Serbia in 1999? Remember the TV pictures of the crashed aircraft in a farmers field with all that fancy stealth technology just laying about, ready to be picked up and reverse engineered by anyone? Well, trickle-down engineering has finally brought once classified aerospace technology to your desktop PC, where essential elements of the mysterious 'black stealth coating' are now applied to heatsinks to improve heat transmission from metal surfaces to air!

Or not... that previous paragraph is pure fiction. Still, this is the connotation Xigmatek seem to be implying with a novel heatsink called the Dark Knight SD1283 Night Hawk Edition and its "stealth technology - low heat signature ceramic coating."

Frustratingly, there's not much Frostytech can conclusively tell you about the 'heat transmission coating' on the outside of what is otherwise a Xigmatek SD1283 tower heatsink. The matt black coating has a texture on par with 400 grit sandpaper, it's fine enough to have been sprayed on, it coats every nook and cranny of the CPU cooler evenly and the material doesn't come off easily when scraped. What exactly the coating is made of, how thermally conductive that material is and what difference this surface treatment makes to heatsink performance are more difficult questions to answer.

  Xigmatek Dark Knight SD1283 Night Hawk Ed. Ceramic Coated Heatsink Review