“So whether you eat or drink or whatever you do, do it all for the glory of God." 1 Corinthians 10:31
This law found in Leviticus 19:28 was part of the separation of the Israelites from their pagan neighbors: Do not cut your bodies for the dead or put tattoo marks on yourselves. I am the LORD. Orthodox Jews still follow the command today. Does it have any bearing for Bible believing Christians?
New Testament epistles and the statements of early church leaders (Acts 15:28) affirm that Christians are not bound to follow Jewish law. When there is scriptural silence, it's difficult to be dogmatic while condemning actions outside of the 10 commandments as sin. If you are trying to make your mind up, consider these next two verses.
1 Corinthians 6:19–20 Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought at a price. Therefore honor God with your body.
Romans 14:23 But whoever has doubts is condemned if he eats, because the eating is not from faith. For whatever does not proceed from faith is sin.
If you can from faith say that you are honoring God with your body through tattooing or piercing it, I believe you have the freedom in Christ to do so. If something seems doubtful to you, it's good to avoid it. Finally, Paul wrote that there is no condemnation to those who are in Christ. If you have tattoos that are obviously worldly, they don't condemn you. Understand that they are now part of your testimony: God has delivered you from your old life of sin, adopted you, and given you new life through the sacrifice of His son Jesus.