Here is an article that claims it is HO HO in American Morse: http://ka8vit.com/special/Why-HI-01.pdf But more importantly, while looking around at old telegrapher's magazines and books, etc, I came across this article from 1902 that uses the word "hams" as senders of "hog-Morse", which is a form of sloppy Morse. I think with all of the debate and discussion of where the word "ham" came from, this is the earliest use of the word that I have seen, in a telegraphy context: https://books.google.com/books?id=-...Q6AEwAHoECAEQAg#v=onepage&q=hog-Morse&f=false
I've never heard of the HEE explanation but it makes sense. One can emphasize the dit-dit accordingly just like the dit-dit that is often sent when ending a QSO.
Why do the Americans think they invented this? It is well known that Ho, Ho as posted by K7jem is the correct and original origin. However it has nothing to do with the slave trade. Its origins, were invented by hams in the polar regions of Scandinavia one Christmas when Santa was spotted on his annual journey to deliver presents before Xmas. As most of you know, "Ho, Ho,' was his jocular cry when he came down chimneys and, or met anyone on his way. The Scandinavian hams soon picked this cheerful sign up and passed the word, 'Ho Ho' as a shorthand for the impending delivery along the length of Scandanavia and the rest of the world as a sign of joy and happiness. To accommodate other religions it has evolved over time into the common Hi Hi or Hee Hee, as an expression laughter and joy. Dave P
I can't ever remember H E E, but always used and heard (though not on in recent years) HI HI. All the explanations and experiences are interesting nonetheless.