Since the XIV Century, this symbol has been the official insignia of the Holy See and is used on the flag of the State of Vatican City, on the coat of arms of the Holy See and on the Vatican seal.
The symbol shows two crossed keys surmounted by the papal tiara or triregnum. Just what the three crowns of the Triple Tiara symbolize is disputed. Some have linked it to the threefold authority of the Supreme Pontiff: Universal Pastor (top), Universal Ecclesiastical Jurisdiction (middle) and Temporal Power (bottom).
Others have given a spiritual interpretation, the three-fold office of Christ, who is Priest, Prophet and King. Other theories suggest the three crowns refer to the ‘Church Militant on earth’, the ‘Church Suffering after death and before heaven’, and the ‘Church Triumphant in eternal reward’. Yet another others suggests they represent the Pope’s roles as lawgiver, judge and teacher.
The iconography of the keys is drawn from the 16th chapter of the Gospel of Matthew where the Apostle Peter, the first pope, receives the keys given by Christ:
“And so I say to you, you are Peter, and upon this rock I will build my church, and the gates of hell shall not prevail against it. I will give you the keys to the kingdom of heaven.
The gold key alludes to the power in the kingdom of the heavens, the silver one indicates the spiritual authority of the papacy on earth. The red cord with the bows that unites the keys represents the bond between the two powers.