IHS is the anglicized rendering of the first three Greek letters in Jesus’ name. In the early Church, especially during the time of the Roman persecution, this became a popular way of writing Jesus’ name as a sort of code. Since then it has become a universally-used insignia and shows up on all types of Catholic religious art and accoutrements. After a few centuries, when the monogram was integrated into the general Latin usage of the Church, many were unacquainted with the original meaning and wrongly believed it meant, in Latin, Iesus Hominum Salvator (Jesus, Savior of Humanity), Iesus Hierosolyma Salvator (Jesus, Savior of Jerusalem), and even the exquisitely banal English version your friend favors, In His Service.