That would, of course, depend on the tattoo. A well placed tattoo saying “mom” or “Jesus” or “America” ETC. would be appropriate. Of course if you are a Christian then the rule of thumb would be I 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 glorify God with your body”.
And I Corinthians 10:31: “So whether you eat or drink or whatever you do, do it all for the glory of God”.
If we make these two verses rules for our lives we will not go wrong.