It is highly common to walk into a Catholic church and see the letters IHS engraved on a crucifix or prominently featured in a stained glass window.
So what do they mean?
In contrary to some popular belief, IHS neither means “I have suffered,” “Jesus Hominum Salvator” nor “In Hoc Signo.”
Appropriately, IHS is called a “Christogram,” because, it is an ancient way of writing the word “Jesus Christ.”
Dating as far back as back as the third century, Christians reduced the name of Jesus by only writing the first three letters of his name in Greek, ΙΗΣ (which is ΙΗΣΟΥΣ in full).
The Greek letter Σ (sigma), is written in the Latin alphabet as an “S,” which resulted in the monogram being commonly represented as ΙΗS.
During the early centuries of the Church it was a secret symbol, often engraved on tombs of Christians. Then, close to the 5th century, Saint Bernadine of Siena went on a preaching campaign to promote the reverence to the Holy Name of Jesus and motivated the Christians to put IHS on the doorways of their homes.
After a century, in 1541 Saint Ignatius adopted the monogram to represent his newly founded order, which is the Society of Jesus. Currently, the symbol spread through the Christian art all over the world.