Motorcycle enthusiasts often say that there’s nothing like the roar of a Harley-Davidson hog. The company agreed and in the late 1990s tried to copyright the sound of its engines roaring into life. Believe it or not, sound copyrights are fairly big (Nokia owns its famous 1990s ringtone for example), but notoriously difficult to obtain.
At the time only 23 of 730,000 active trademarks relate to sounds or noises. Harley-Davidson ultimately dropped its claim, probably because it would have been nearly impossible to prove the sound was unique to their engines.