Sonic Trademarks: The Case of the Wacky Quackers

From The Times:

At issue is a “sound mark,” the auditory equivalent of a trademark, which Ride the Ducks says it holds on a quack created by a yellow bill-shaped kazoo (called a Wacky Quacker) and which it says Bay Quackers has violated by using a similar kazoo that creates an identical quack.... such sound marks (are) fairly uncommon, with only about 150 registered, a short list that includes the Ride the Ducks quack, the MGM lion’s roar and NBC’s signature chimes.

More on "sound trademarks" here, with audio samples (including more quacking), here.