The devil decal is in excellent and secure condition. Consideration should be given to whether or not this has become part of the guitar's soul or not; While I ascertain the feasibility of removing the decal without damage to the guitar's finish. Decals can almost always be removed; But often a long a tedious process of doing so without damagaing the guitar's finish. Sometimes decals will come right off after progressively teasing some light innocuous oil under and lifted tab and slowly peeling it back, hopefully without tearing the decal that acts as a good "handle" to for a continuous removal peel-off.
Again, the dull smudging is a protective coat I put on the guitar's finish and hardware some time ago, and will clean right off. The finish will then be replenished with proper oil that will also act as a polish, makeing the guitar quite handsome again.