What kind of shapes are in the belt that Lame Deer's grandmother made that is mentioned in Chapter 6 and what do these shapes represent?

In the belt that Lame Deer's grandmother made there are rectangles with one line missing which represent horses' tracks, there is a shape that represents a horse killed in battle and its rider rescued by Lame Deer's grandfather. There are are two triangles that represent arrows shot at an enemy. Basically, the belt tells of a battle.