Final answer:
When signing "wind (very windy)", the cheeks are used to represent the force of the wind puffing the cheeks out.
Step-by-step explanation:
The part of the face used when signing "wind (very windy)" is the cheeks. This incorporates a lateral movement of the cheeks, which is also a common movement used for actions like sucking on a straw or compressing air in the mouth while blowing. This action is representative of showing how wind can cause one's cheeks to puff out as if being blown by a strong wind.