Do you have any idea what the cranium of Thor is for?
There is not much told regarding the purpose of this under its names Þórrsauga og heilabú (Thor’s eye and head). However it is often given along with another simple looking symbol called Þórshamar
hammer). There it is described saying it is for revealing or summoning a thief and other magic.
Jón Arnason suggests they are one in the same symbol. Jochum Eggertsson described how both derive their magic by use of a needle piercing through the eye of Thor (as depicted in the symbols) which would cause a thief to loose their sight - a bit like a voodoo doll - unless the thief came forward and confessed.
Icelanders were a very poor bunch of folk in the middle-ages, so many of their galdrastafir relate to preventing theft or revealing thieves.