The Greek letter iota is represented by I, and the eta by H, while the Greek letter sigma is either in its lunate form, represented by C, or its final form, represented by S. Because the Latin-alphabet letters I and J were not systematically distinguished until the 17th century, “JHS” and “JHC” are equivalent to “IHS” and “IHC”.
“IHS” is sometimes interpreted as meaning “Jesus Hominum (or Hierosolymae) Salvator”, (“Jesus, Saviour of men [or: of Jerusalem]” in Latin) or connected with In Hoc Signo. Such interpretations are known as backronyms. Used in Latin since the seventh century, the first use of IHS in an English document dates from the fourteenth century, in The vision of William concerning Piers Plowman. In the 15th century, Saint Bernardino of Siena popularized the use of the three letters on the background of a blazing sun to displace both popular pagan symbols and seals of political factions like the Guelphs and Ghibellines in public spaces (see Feast of the Holy Name of Jesus). The IHS monogram with the H surmounted by a cross above three nails and surrounded by a Sun is the emblem of the Jesuits, according to tradition introduced by Ignatius of Loyola in 1541. English-language interpretations of “IHS” have included “In His Service”.
The design has been borrowed from the interwoven IHS contained on Saint-Martin’s Church, L’Isle-Adam, Val-d’Oise