Blowing/hunting/signal horns were used in many different ways. As a signal horn they were used to pass information between farms, such as a fire or Indian attack with short and long blasts, similar to Morse code. Also used in Deer and Fox hunting, to tell the direction the animal is headed, Fox is killed, yes/no answers, etc...
These horns are still used in parts of the US today. I was contacted by a fellow from Louisiana, to make a mouth piece that he could get different tones from, I made him three and two worked for him. He must have been fairly talented because he said he could get 5 distinctly different sounds from them.
Take a look at the link below from the HCHs site, you will see a number of articles listed on blowing horns.
They are not toys or oddities but real tools used in the field or at the homestead.
http://www.hornguild.org/the-horn-book/index-of-horn-book-articles/ Tim C.
PS: It differs from a Powder horn because the bell end is open and it has a mouth piece.TC