In Handbook (fig. 61,i-j) it appears as point-to-point chevrons on the cheeks.
Written language is thus a point-to-point equivalence, to borrow a mathematical phrase, to its spoken counterpart.
And these two classes sustain a point-to-point correspondence to each other—they are correlated.
The design name given, "butterfly," probably applies to the point-to-point large solid triangles, possibly to the rhomboids.