IHS carving in the Roman catacombs

The three nails pictured on some examples represent the nails of the crucifix.

The IHS is a symbolic monogram of Christ used by the Roman Catholic Church. This monogram consists of the Greek letters iota, eta, and sigma, the first three letters of the name Iesous (Greek for Jesus), the letters of which are also used to spell out the phrase "Iesous Hominum Salvator," "Jesus, savior of man." It relates to the story of Constantine, whose vision of the Chi-Rho was recorded by Church Father Eusebius. In the vision, Constantine was reported to have heard a voice proclaim, "In this symbol, thouse shalt conquer." Therefore, the IHS has also stood for "In Hoc Signo," in this sign.

The symbol as it appears at right originated in Rome with the early Christians, and was popularized in the fifteenth century by Franciscan disciple Bernardine of Sienna, who promoted it as a symbol of peace.