Can christians put tattoos on their skin?

True Christians follow The Bible and understand that although God is a loving God, he has standards that need to be upkept in order to remain in God's Love. The opposite is true, one can fall out of God's love.

See Leviticus 19:28 to find out God's commandment to the nation of Israel in regards to tattoos.

Also consider the principle found in Romans 12:1 - "Consequently I entreat YOU by the compassions of God, brothers, to present YOUR bodies a sacrifice living, holy, acceptable to God, a sacred service with YOUR power of reason."