What does INRI on crucifixes mean?

The Latin initials INRI represent “Iesus Nazarenus Rex Iudaeorum" (Jesus of Nazareth King of the Jews). In keeping with Roman crucifixion practices, Pilate had Christ’s name and “crime against Rome” nailed to the cross as a warning to others. This “titulum” was among the items St. Helena discovered in Jerusalem, and it is preserved along with other relics of the Passion in the Church of the Holy Cross in Jerusalem in Rome.
John 19:19 Pilate also wrote a title and put it on the cross; it read, “Jesus of Nazareth, the King of the Jews.”