These three letters are called a Christogram

These three letters are called a Christogram, which is a monogram or a combination of letters that form an abbreviation for the name of Jesus Christ. It is an ancient way of writing the name Jesus that dates back to the third century. The Greek letters I H Σ (iota eta sigma) are the first three letters of ΙΗΣΟΥΣ, the Greek name of Jesus. The Greek letter Σ (sigma) is written as an S in Latin and is how we write the letter today. In early Christianity I H S was a secret symbol to help identify fellow Christians. In the 1400s Christians put the symbol on their doorways to identify their dwelling as a Christian home. Some translate the three letters as a Latin phrase, Iesus Hominum Salvator, meaning “Jesus Savior of Mankind.” The Christogram I H S is usually found in Lutheran and Roman Catholic churches and cemeteries.

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