Look for these words in the facsimilie below...
What are the letters supposed to be in the Pope's crown, and what do they signify, if anything?
The letters inscribed in the Pope's mitre are these: Vicarius Filii Dei, which is the Latin for the Vicar of the Son of God. Catholics hold that the church which is a visible society must have a visible head. Christ, before His ascension into heaven, appointed St. Peter to act as His representative. Upon the death of Peter the man who succeeded to the office of Peter as Bishop of Rome, was recognized as the head of the Church. Hence to the Bishop of Rome, as head of the Church, was given the title "Vicar of Christ."
Enemies of the Papacy denounce this title as a malicious assumption. But the Bible informs us that Christ did not only give His Church authority to teach, but also to rule. Laying claim to the authority to rule in Christ's spiritual kingdom, in Christ's stead, is not a whit more malicious than laying claim to the authority to teach in Christ's name. And this every Christian minister does.