It seems that Peter is not particularly fond of his tattoos : a subzero and eagle on his right arm, a panther/mountain lion on his left, a black widow spider just below his right hip, and a small but mysterious conglomeration of symbols and symbolism on his chest:

The meaning of his chest tattoo was widely unknown until he let inquiring minds know on the
Official Type O Negative Website Q&A Page:

"The tattoo on my chest was a combination of how my ex-wife and I used to identify ourselves.  Meaning, she considered herself to be a witch and right she was; instead of signing her name, she would use a pentangle.  And I, being the dickhead that I was, (and still am), had a severe inferiority complex and the symbol I had chosen was an ancient Greek symbol for Jesus Christ, in a crude attempt to associate myself with a powerful being."