Mine came off when half of the screws snapped off. Not an issue if it's not going to be reused.
Grab the screw head with a pair of vice grips and twist them off. Or if you want to save the emblem, get an oxy-acetylene torch with a small tip and heat the screw heads to a dull red then let them cool. Typically that will allow them to come off. PB Blaster can't help much here as it can't get to the captive nuts in the emblem (well unless you dipped the whole front of the hood in it.)
