Painting in the Church of the Gesu has 3 letters, what do they mean?

Question

Hello,

See the image at this link:
http://upload.wikimedia.org/wikipedia/commons/9/99/Rome-EgliseGesu-Fresque.jpg

Its the image of Giovanni Battista Gaulli's painting (or fresco) in the Church of the Gesu - painted on the ceiling

If you zoom in to the "light" in the center of the image, you can see a small golden cross and " I H S " below that (copy and paste in paint if its not big enough).

What do those 3 letters mean? Seems kinda strange to have left 3 letters there when nobody can read it without closing up on it. The painting is in the ceiling and the letters are so faint that nobody can see it even if they're looking for it!

@ "guess who at large" - hey, great answer but i'd like to wait a bit and see if i get others....

Answer 1

In the Latin-speaking Christianity of medieval Western Europe (and so among Catholics and many Protestants today), the most common Christogram is "IHS" or "IHC", derived from the first three letters of the Greek name of Jesus, iota-eta-sigma or ΙΗΣ. Here the Greek letter eta was transliterated as the letter H in the Latin-speaking West (Greek eta and Latin-alphabet H had the same visual appearance and shared a common historical origin), while the Greek letter sigma was either transliterated as the Latin letter C (due to the visually-similar form of the lunate sigma), or as Latin S (since these letters of the two alphabets wrote the same sound). 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".

http://en.wikipedia.org/wiki/Christogram
http://www.nomensanctum.org/Web%20Pages/Holy%20Name%20Logo/monogram.htm