The symbol has older occult
or anti-christian associations and it
was a ‘symbol of death’.
This fifth century illustration depicts Peter crucified
upside-down. The inverted crucifix was known for
centuries as the‘Nero cross’ from the roman reign
of the emperor nero (54-68 A.D.)
in the middle ages the ‘Nero cross’ was adapted
in satanists rituals.
It can also be seen as composed of a tyr rune,
or by the rune, turned upside down
(in German ‘Todesrune’/ The Rune of Death.)