Catholic is a term that is used indicate Christendom as a whole. Christianity is an important and is the first largest world religion with more than 2.4 billions population. There is no restrictions for a catholic to get inked.
With no restriction on inking, catholic people tend to get a catholic related tattoos.
Catholic tattoos are mostly about Cross, Jesus, Virgin Marry (Jesus's mother). These types of tattoos are totally related to their religion and their believes.
Catholics are not restricted with getting inked but the tattoo should not be immoral or Satanic. There should not be any opposition to teaching of Christianity. Catholic tattoos revolve around the teaching and believes of their religion.