Ask a Harley rider what makes a Harley a Harley and, eventually, they'll get to the sound. The low, uneven, loping rumble of the engine at idle — potato-potato-potato, as enthusiasts have described it for decades. It's not a metaphor. It's a genuinely distinctive noise, produced by a specific quirk of engineering. And in 1994, Harley-Davidson decided it wanted to own that noise the way it owned its logo.
You Can Trademark a Sound
The idea isn't as strange as it first sounds. Trademarks protect anything that identifies the source of a product to consumers — and that can include a sound, as long as the sound does the identifying. The MGM lion's roar is a registered trademark. So are the NBC chimes, the THX "deep note," and the Intel bong. When you hear those sounds, you know instantly which company made them. That's precisely what a trademark is for.
So Harley's application wasn't absurd on its face. The company argued that its exhaust sound was as recognizable as any of those — that a rider or bystander could identify a Harley by ear alone, without seeing the bike. If true, the sound functioned as a source identifier, which is the whole test.
In February 1994, Harley-Davidson filed a trademark application describing the sound: the "exhaust sound of applicant's motorcycles, produced by V-twin, common crankpin motorcycle engines when the goods are in use."
Why a Harley sounds like that: The rumble comes from the engine's design. Harley's V-twin engine has both connecting rods sharing a single crankpin, set at a 45-degree angle. The result is an uneven firing interval — the cylinders fire, then there's a pause — which produces the syncopated potato-potato beat instead of a smooth hum. The sound is a byproduct of the mechanics.
Nine Competitors Said No
The application ran straight into a wall. Nine rival motorcycle manufacturers — including Honda, Kawasaki, Suzuki, and Yamaha — filed oppositions with the U.S. Patent and Trademark Office. Their objection cut to the heart of the case: the sound Harley wanted to own wasn't unique to Harley. It was the natural result of a common crankpin V-twin engine, and other manufacturers built motorcycles with that same engine configuration. Those bikes made a similar sound because they were built the same way.
This is the fatal problem for a lot of would-be sound and shape trademarks: functionality. Trademark law will not let a company monopolize a feature that exists for functional reasons rather than for branding. If the potato-potato sound is simply what a 45-degree common-crankpin V-twin does, then granting Harley a trademark on it would effectively hand Harley control over an engine design that anyone is free to use. You can't trademark your way to an engineering monopoly.
Harley's counter-argument was that even if others could make the sound, consumers still associated it specifically with Harley-Davidson through decades of marketing and cultural presence. Maybe the sound was functional in origin, but it had also become a brand signal. Both things could be true.
Six Years, Then a Quiet Retreat
The opposition proceeding ground on for six years. It was expensive, it was slow, and it was uncertain — the functionality objection was strong, and Harley faced the real possibility of a formal ruling that the sound was unprotectable, which would have been worse than no ruling at all. A loss on the record would invite competitors to lean into the sound.
In 2000, Harley-Davidson withdrew the application. The company's official framing was pragmatic: the litigation was consuming resources, everyone already knew a Harley when they heard one, and a piece of paper from the USPTO wasn't going to change that. As one executive put it at the time, if their customers knew the sound was a Harley, the company didn't need a registration to prove it.
It was a face-saving exit from a case Harley might well have lost. The sound trademark was never granted, and to this day the potato-potato rumble belongs to no one — which means, legally, it belongs to anyone who builds an engine that makes it.
What the Non-Trademark Is Worth
Here's the twist: Harley didn't really need the win. The failed application generated years of press coverage, all of it reinforcing exactly the association Harley wanted — that the sound is the brand. The company spent six years and a fortune in legal fees on a trademark it never got, and arguably came out ahead in brand terms anyway, because the whole saga told the world that Harley cared enough about its sound to fight for it.
The legal lesson is cleaner. Sound marks are real and registrable — the NBC chimes prove it. But a sound that arises from how a product functions, rather than from a deliberate branding choice, runs into the functionality doctrine, the same barrier that stops companies from trademarking useful shapes and colors. Kit Kat couldn't own the four-finger bar because the shape was functional. Harley couldn't own the rumble because the sound was mechanical. In trademark law, the things that come free with the engineering tend to stay free.
Frequently Asked Questions
Can you actually trademark a sound?
Yes. A sound can be a registered trademark if it identifies the source of a product to consumers. The MGM lion's roar, the NBC three-note chime, the THX deep note, and the Intel bong are all registered sound marks.
Why did Harley-Davidson's sound trademark fail?
Because of the functionality doctrine. The potato-potato sound is a natural byproduct of a common-crankpin 45-degree V-twin engine — an engine configuration other manufacturers also use. Nine competitors opposed, arguing the sound wasn't unique to Harley but a result of shared engineering. Harley withdrew the application in 2000 after a six-year fight.
What makes a Harley engine sound like that?
The V-twin engine's two connecting rods share a single crankpin at a 45-degree angle, producing an uneven firing interval. Instead of a smooth hum, the cylinders fire with a pause between them, creating the syncopated potato-potato rhythm.
Does anyone own the Harley sound now?
No. The trademark was never granted, so the sound is legally unprotected. Any manufacturer that builds an engine of the same configuration can produce a similar sound without infringing anything.