There is some controversy concerning what is written on the
popes Miter, however according to many; Vicarius Filii Dei is
written on his miter. Vicarius Filii Dei means: The representative
of the Son of God.
Sadly the controversy is caused by the fact that this story
(possibly invented by the Seventh Day Adventists tho used by many
extremist Protestant groups) is utterly untrue.
The phrase is supposed to have been written on (an unspecified)
papal tiara (not mitre); sadly for conspiracy theorists there is no
writing on any of the papal tiaras (they are all still extant). The
"evidence" is supposed to be contained in an early photograph of a
papal corronation; the photograph exists but its quality is such
that it would be impossible to read any engraving on the tiara
(even if it existed).
Sadly despite the facts in the matter it will not stop this
story from being trotted out as fact by people like Jack Chick.