Final answer:
The penalty for not wearing protective headgear while riding a motorcycle on a highway or public street illegally is a traffic violation that can result in a fine.
Step-by-step explanation:
In most states, the penalty for not wearing protective headgear while riding a motorcycle on a highway or public street illegally is a traffic violation and can result in a fine. However, the specific penalty may vary depending on the state and its laws regarding motorcycle safety. It is important to note that wearing protective headgear, such as a safety helmet, is crucial for preventing head injuries and ensuring rider safety.