It is an expression of what they see in the world around them, I think. A way of dealing with the unfairness of class separations.

A: Skulls are demonic
+ B: She has a skull
= C: She is demonic

D: Demons things are bad
+ E: Demonic things should be banned
= F: She should be banned.

She can chose not to buy them.

@Jmatts: excellent!
my son loves to where skulls on his shirt or wherever.
we all have skulls, i fail to see how they represent anything demonic. now perhaps if they have horns in them???

Christians fear the reality of death, hence they cling to religion to ease their fears.

We have calaveras (painted skulls) in the Mexican tradition all over the house, all year round. It's a cultural issue, not "demonic."

God is love.
Love is blind.
Ray Charles is God.

the skull and crossbones is a symbol of john the baptist of the catholic church, before that it probably belonged to the pagans

Jesus was crucified on Calvary or Golgotha, the "place of the skulls."