Triangles and diamonds and squares, oh my! And you thought that music notes only came in one shape. In fact, there's a whole singing movement, appropriately called "shape-note singing," in which singers read a variety of different note shapes--each one corresponding to a different syllable. This most unusual form of choral singing has deep roots in American history and a devoted following all over the country, where shape-note singers may gather for a few hours or for all-day "singings."
Source: Chorus Community