If you have had "relations" with someone, but have asked forgiveness and seen the errors of your ways and want to rededicated yourself to God, would it be considered wrong to wear a purity ring or something along those lines?
If you are doing so to make it appear that your are something that you are not, then it would be wrong because it would be a deception. But if you are wearing it to announce that you not going to have sex again before you are married to a real man, then there isn't anything wrong.
People can and do change. That is what Christianity is about. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God" (I Corinthians 6:9-11). There were people at Corinth who had done what we would call awful things, but because they gave their lives over to Christ, being obedient to his teachings, they changed. That is why Paul said becoming a Christian is like rising to a new life. "Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life" (Romans 6:3-4).
"Beloved, now we are children of God; and it has not yet been revealed what we shall be, but we know that when He is revealed, we shall be like Him, for we shall see Him as He is. And everyone who has this hope in Him purifies himself, just as He is pure" (I John 3:2-3). Being a Christian is about making your life more like our Lord. The point isn't that you've sinned, it is that you have renounced sin. Make your life such that no one seeing you would guess that you once behaved badly. "For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter" (II Corinthians 7:11).