Final answer:
The sign for 'Stop' in non-verbal communication is best described by holding the palm outward, which is the gesture universally recognized to signal a halt in action.
Step-by-step explanation:
The sign for the word "Stop" is appropriately described by holding the palm outward. Therefore, the correct answer is D. Holding palm outward. This action is often universally recognized as a signal to halt or cease current actions. It is similar to how traffic signs function, which are a form of symbolic communication; for instance, the red octagonal traffic stop sign signals vehicles to stop. In human communication, the gesture of holding one's palm outward towards another individual conveys a clear message to stop without the need for verbal language.