Does the idea of defiling the body still apply if the tattoo is a simple religious reference?

"Christians believe that getting a tattoo is defiling your body."

Most Christians don't believe that, actually. That law is from the old covenant, it never applied to Christians.

tattoos were prohibited in OT times because the were associated with Paganism. Christians have the freedom to where a tattoo if they're conscience permits. It should be a tattoo consistent with holiness.
--For why is my freedom being judged by another’s conscience? (1 Corinthians 10:29)
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If your god knows everything..why do you need to overtly wear a cross or tat.?

There is nothing in the bible against tattoos. Depends on the person, cutlure, history, etc.

The body is the Lord's.

“For truly, I say to you, till heaven and earth pass away, not an iota, not a dot, will pass the law until all is accomplished. Whoever then relaxes one of the least of these commandments and teaches men so, shall be called least in the kingdom of heaven; but he who does them and teaches them shall be called great in the kingdom of heaven.” — Matthew 5:18-19

So you think God gave his people instructions on how to be godly, and then just changed his mind because of fashion? Go ahead, explain to God that all the kids are doing it these days, I'm sure he'll change his rules, just for you.