There was a knuckleduster knife made for Brit commandos in North Africa during WW2 that might fit the bill. The blade part was straight like a tanto and didn't have a handguard (Crossguard?). The knuckles were solid brass and had the appearance of a human skull, when laid flat with the cutting edge towards you.
If this seems familiar, I'd get it if only for historical value. 'Course it might be a fake, but I can't imagine an original would be worth enough to bother faking.