According to New Testament of the Bible, (John 19:19 and Matthew 27:37), Pontius Pilate decreed that a placard be affixed to the Cross, with the text (in Hebrew, Greek and Latin): "Jesus of Nazareth, King of the Jews". In Latin, the text was Iesus Nazaraeus Rex Iudaeorum, usually abbreviated I.N.R.I..
As such, the four-letter abbreviation has been repeatedly used in religious art and architecture throughout Christianity's history. In all periods, however, the abbreviation has also often been used for other purposes. The Italian carbonari reinterpreted "I.N.R.I." to mean Iustum Necare Reges Italiae ("It is just to slay the kings of Italy"). It has also been creatively interpreted (when used on French Jesuit colleges) as Ici Nous Rendons Imbéciles ("Here we make idiots of people"). At the coronation of Napoleon in Milan , it was interpreted as Imperator Napoleon Rex Italorum ("Emperor Napoleon, King of the Italians").
Not every interpretation shows as much wit, however. The (17th century) French Marquis de Gèvre fancied himself a great connoisseur of art. One day, in the royal galleries, he observed a series of pictures of the Crucifixion, and remarked that they were all by the same painter, "Monsieur Inri". :-)