Looks like a factory cancelation mark used for reject dice. I have several dice with this mark and most of them have other obvious signs of not being finished or otherwise imperfect in some way. Reject dice do not get throwen away. They get stamped with a logo (sometimes of a long gone casino) and tosed in the bin to sell as souviner dice.
I have as yet been unable to find a casino that used that mark to cancel thier dice. Most casinos use a vice punch that cuts a small circle into the dice but no gold foil. Reject dice can also be found with a gold "XX" on the four side and most often with a plain "VOID" stamped into the 4 side.