The upside down cross tattoo is a popular symbol in contemporary tattoo culture. It is often used to make a statement about rebellion or challenge the norms of traditional Christianity. Its origin is not entirely clear, but one popular belief is that it was adopted by Medieval Knights and Crusaders as a symbol of humility. They would flip the traditional Christian cross upside down, to show that they had given up the materialism of this world and were humbly serving God. In the present day, people often use this symbol to express their individualism and non-conformity to traditional beliefs.