Wind is represented on the upper right and left parts of the back of the guitar. The wind on the left, keeping in theme with the front of the guitar, represents Yang or the masculine, and the wind on the right represents Yin or the feminine. The wind design was actually based on the symbol for "wind" from the I Ching:

And then stretched to make a long line which if you look closely you will see breaks in the line of the swirling wind on the guitar. It  is representative of the lower broken line in the trigram, which is the weak yin line outside at the bottom. The motivation is said to be soft and penetrating. The image is grass and wind, the wind does not harm the rooted grass: