Good post and thanks for sharing your opinion. Though the Bible does not talk about tattoo but what are side effect of tattoo. If the effect comes, are we going to say it is from God or we are tempted? James 1:13-14.
That the world are using tattoo does not mean we have to use it. Don't forget that we should not be unequally yoked with unbeliever 2 Corinthians 6:14. And this evangelism, is about God who convinces heart not any human work or effort.
I will therefore say tattooing for gospel should not be encouraged.