Shapes were added to the note heads in written music to help singers find pitches within major and minor scales without the use of more complex information found in key signatures on the staff. The idea behind shape notes is that the parts of a vocal work can be learned more quickly and easily if the music is printed in shapes that match up with the solfege syllables with which the notes of the musical scale are sung.
Four shape system:
Seven shape system (for showoffs):
Fun fact: The practice of singing music to syllables designating pitch goes back to about AD 1000. I did not know that.
So shape note singing was invented and now huge groups of people could divide up complex melodies to accompany their religious hymns and the grey area between accuracy and imperfection that was created by their lack of training or ability makes shape note singing eerily heavy. Instruments are overrated. No distorted guitar is going to get as heavy as fifty old southerners shouting their lungs our in some decrepit barn-church. Imagine if you were walking alone through the woods in 1804 and you started to hear this shit:
Anyway, if you're into it you can get some here. Jam it loud first thing in the morning when you get to work. Everyone thinks you're a weirdo anyway.