Whew, thanks, Hiero. I was wondering how many incorrect explanations we would go thru before someone gave the right one.
IHS is a “monogram” or abbreviation for the name of our Lord Jesus; it’s the first 3 letters of His name in Greek. It’s that simple.
Look at Post 175 (directly after your answer). Note that it reads IHS, not iota-eta-sigma. So, those are Latin letters, not Greek ones. So, It is not a monogram of +Jesus+’ name, but as other insist and I agree, IHS, in hoc signo [vinces], referring to Constantine’s symbol at the Battle of Milvian Bridge.
Besides, Georgetown was founded by Roman Catholics, not Greek Orthodox. It would be wonderful if they did adopt some Eastern symbology, but unusual and probably even at this point unprecedented.