Question: What does "IHS" refer to? What does "INRI" stand for?
Answer: IHS is a monogram for the name of Jesus Christ. INRI stands for "Jesus of Nazareth, the King of the Jews".
Why do these start with the letter I instead of J? Find out by reading more:
http://www.newadvent.org/cathen/07649a.htm
http://www.christiananswers.net/q-eden/edn-t024.html
http://www.thenazareneway.com/inri_the_inscription_explained.htm