This is more for my knowledge and for others. I know that if a person who is of the book has had tattoo's but they later regret and repent, then that is ok and as long as they do not continue down that path again.
What if there is a person who has a tattoo on their back but it is of a cross (to their faith)? We know that worshipping idols and such is haram and a sin but if it is a symbol of their faith then what is the ruling?
Of course we know that it is better to be with a Muslim of the same faith for many reasons but this is more of a general question more than anything and to see if it is permissible for a Muslim to be married to such a person.