A service mark differs from a trademark in that the mark is used on the advertising of the service rather than on the packaging or delivery of the service, since there is generally no "package" to place the mark on, which is the practice for trademarks. Transportation carriers would paint their service marks on their vehicles, such as on planes or buses. Personal service providers would put their service marks on their delivery vehicles, such as on the trucks of plumbers or on moving vans. However, if the service deals with communications, it is possible to use a service mark consisting of a sound (a sound mark) in the process of delivering the service. This has been done in the case of AT&T, which uses a tone sound followed by a woman speaking the company's name to identify its long distance service, and MGM has used the sound of a lion's roar for its motion pictures.
Under U.S. law, service marks have a different standard of use in order to count as a use in commerce, which is necessary to complete registration and to stop infringement by competitors. A trademark normally needs to be used on or directly in association with the sale of goods, such as on a store display. As services are not defined by a concrete product, use of a service mark in advertisements is instead accepted as a use in commerce.