If motorcyclists are a unique breed, Harley-Davidson motorcyclists must be considered a cult unto themselves. They have transformed the hobby of motorcycling into a lifestyle, replete with clubs, clothing, and a distinct “biker culture.”  The official Harley-Davidson web page describes the Harley history and allure:
In 1903, three Davidson brothers and their friend, Bill Harley, started a rumble heard ‘round the world. Their first motorcycle was the start of a unique combination of people and machines. Through the decades, Harley-Davidson motorcycles have had the ability to generate emotion. The excitement of racing, the peacefulness of a ride down a country lane, the pleasant symphony of a handful of bikes rumbling down Main Street, the exhilaration of switchbacks on a mountain road, but most of all, the camaraderie of the people who share the same love for Harley-Davidson motorcycles. The Brotherhood. The Sisterhood. The Family. It’s time to come home. 
The Harley-Davidson corporation’s ability to evangelize the Harley lifestyle– as on the company’s website–without alienating a customer-base which prides itself on being free-spirited and countercultural has been a testament to its marketing shrewdness. However, in a business expansion which probably irked the hardcore Harley faithful, the company now manufactures or licenses jewelry, watches, clothing, and a chain of “lifestyle” restaurants called the Harley-Davidson Cafe. 
In every commercial enterprise Harley-Davidson has undertaken, the company has ensured that the integrity of its trade name and various trademarks in the marketplace is vigilantly protected. Indeed, Harley has successfully litigated trademark infringement cases in federal courtrooms across the country.  Interestingly, much of this litigation has taken place within the past five to ten years. This development has a purely economic reason. Since the 1980’s, when the U.S. motorcycle market was dominated by Japanese manufacturers such as Honda, Yamaha and Suzuki, Harley-Davidson has enjoyed a remarkable resurgence of business–to the tune of approximately $1.5 billion in revenues.  This cash has enabled Harley to pursue trademark infringers with a renewed zeal.
Harley-Davidson’s most recent endeavor to secure trademark protection is not only its most unconventional, it is also arguably, the most unusual and provocative trademark application ever filed with the U.S. Patent and Trademark Office (PTO). On February 1, 1994, Harley filed a registration for a trademark, then already in use, with the following description: “THE MARK CONSISTS OF THE EXHAUST SOUND OF APPLICANT’S MOTORCYCLES, PRODUCED BY V-TWIN, COMMON CRANKPIN MOTORCYCLE ENGINES WHEN THE GOODS ARE IN USE.”  Put simply, Harley was attempting to trademark the sound of its motorcycles; which, of course, begs the question, can a manufacturer trademark the exhaust roar of its motor vehicle?
Michael B. Sapherstein*