Pirate nails! Or more specifically, skull and crossbone nails.
I got this stamping plate from this seller on ebay- he doesn't have anything listed at the moment, but it's worth checking him out as he has random plates all the time and they're pretty sweet. This one is QA8- it stamps well, considering I thought it would be very dodgy!
I used Color Club Revvvolution as the base- hoping that a little charcoal holo-y goodness would peep out between the skulls- but that was a big ol' fail, it was too obscured by the Konad white polish I used. What's that I hear you cry? You want to see Revvvolution by itself?
Go on then...