No, Harley Davidson does not have a monopoly on the bar and shield motorcycle gas tank logo. While the bar and shield logo is strongly associated with Harley Davidson motorcycles and is a registered trademark of the company, it does not grant them a monopoly over all similar designs or logos in the motorcycle industry.
Trademark protection is granted to specific logos, designs, or brand names to prevent confusion among consumers and to protect the intellectual property of a company. While Harley Davidson has registered its bar and shield logo as a trademark, it does not mean that no other company or entity can use a similar design.
The extent to which a similar logo or design might be considered an infringement would depend on factors such as the similarity of the design, the industry or context in which it is used, and the potential for consumer confusion.
In summary, while Harley Davidson has trademark protection for its specific bar and shield logo, it does not mean they have a complete monopoly over all similar designs.