It is a Sin from the Old testament. Most modern Christian's don't follow it...because in the same book referenced above, you also shouldn't wear most clothes made today, because they are a blend of materials....I think that the Bible means for you not to have a tattoo that you intend on worshiping as an idol....it should not take the place of God or Christ in your heart, and also should not be something you show off as a mark to make people worship you...and I use worship loosely there meaning you shouldn't do it for glory or gratitude....if you get a tattoo it should be something you want to do for you.
Tattoo's are very common, especially in the world we live in today. People get tattoo's for many different reasons, yet the Bible explains God's view on tattoo's.(Leviticus 19:28) Having a permanent mark or design on the skin made by cutting the skin to produce scars or by inserting coloring matter under the skin was common among Egyptians in Bible times, they would tattoo the names or symbols on their breast or arms. However, we want to have proper respect for the human body as God’s creation, to be used in honoring him. (Deuteronomy 14:1) Self-mutilation shows disrespect for the human body, may be connected with false religion, and as true christians, this must be avoided.
There was an episode of Midsomer Murders in which a female vicar wore a series of T-shirts, depending on what she was doing at any particular time.
One read, "Shopping for Jesus" and she stopped to evangelise any shoppers that came within range, another read "Jogging for Jesus" which she wore when she was running. Perhaps you could emulate her and get a tattoo that said something like, "Tattoos for Jesus" or "Billboard for Jesus". That would qualify as witnessing and could hardly be a sin.
I don't think the Midsomer vicar had a tattoo although, toward the end of the show when she came upon a van parked in a cow pasture with it's doors open, she leapfrogged in enthusiastically and had it away with one of her parishioners. I doubt if she was wearing a T-shirt while she was doing that but may have had a tattoo that said, "Procreating for Jesus."
I say no as long as U don't put anything that is satanic, a lot of Christians (me included) have n get tattoos, I realize the OT, Lev 19.28 speaks against it, we were under the law. Rom 10.4 says, Christ is the END of the LAW for righteousness to everyone who believes. Also read Gal 3.23~25, Eph 2.15. 1Cor says that everything U do, do for the glory of God, Rom 14.23 says, But whoever has doubt is condemned if he eats because the eating is not from faith. For whatever does not proceed from faith is sin. Is (to U) getting a tat give U conviction or not? This is a matter between U and your Maker, not a matter between U n someone else, no one can condemn U, only Christ if U feel in your heart that He's telling U not too. A lot of Christians will disagree but I hope this helps.