They could be an occasion to the sin of pride. It calls attention to the 'me' in a person, even if the tattoo is meant to make a statement, religious included. It diverts the attention from the intended purpose of the body's creation.. Among others, the body and it's appendages are the means in this world to carry the task of persuasion, to focus the world on Divine things, and what He desires through our moral conduct. The human body is the temple of the Holy Spirit. If one wishes to adorn that temple, then he could ensure the inner decor(disposition) pleases the eye of God. On creation it initially came decorated in the image of God. Nothing gave pleasure to God more than the likeness of Him painted on that blank canvas. The angels must have been awed by this work of art destined for mighty deeds. The Holy Spirit ensures that if the person strives to keep himself untainted, inwardly and outwardly, he will draw others to him as an example of what God desires. We can tell that it is a progression to 'self''. A decoration must be seen, and the devil had this intent clouded for the time being. The tattoo went from an ambiguous swirl in a discreet spot, or ankle or foot, but now a decorated sign or sleezy billboard. It is a vector that directs the eye to an already over exposed discreet area. I have seen this at mass. Before the priest at communion, the Eucharist now before the recipient, is being exposed to the decorated cleavage within inches from him. Tattoos were used in many cultures, for rank, for tribe identification, even for complete decoration has in the Polynesia. But now this is the Holy age. We know of the conniving of the devil and his having us detracted, and this is just one way of his exploitation.