Your B&H invoice will say whether the lens is grey market or not. B&H sells grey market, but they are pretty clear about it. Since you're still well within the warranty period, I assume you still have your purchase receipt (this is what you need for Nikon USA, not the worthless warranty card. ).
If you have a warranty card from Nikon USA (not just "Nikon"), then that would be pretty definitive that yours is a Nikon USA lens, not a grey market lens. Keep in mind that other markets offer 5-year warranties as well, so do confirm that the warranty is issued by Nikon USA with US-based addresses for authorized service centers.