Use double sided automotive tape.
All car badges are held on with it, it doesn't melt off in the heat, and you can guarantee that some prick will steal your badge one day, it's better to have it stuck there lightly, (as opposed to liquid nails) so they do less damage when they steal it...
If you stick it on the grille, and its ultra hard to remove, the person who tries to pinch it will crack the shits and just smash the grille to get it off.