On Jan. 8, the U.S. Patent and Trademark Office granted Apple Inc. a trademark for the three-dimensional shape of its iPod media player.

This was more than a recognition of an innovative product design. It also was Apple's capping piece in a multiyear marketing and legal campaign that pushed intellectual-property rights to new competitive advantage for the company.

In many ways, Apple is benefiting from an expansion of U.S. trademark rights, beyond the traditional names, images, logos and two-dimensional symbols trademarks usually secure. In recent years, trademarks have been granted for such things as product shapes, colors and scents that companies can claim are linked exclusively to the source company in consumers' minds.

These nontraditional marks are difficult to obtain. But unlike more commonly used utility and design patents, which exist to cover functions and the ornamental look and feel of products and expire after a set number of years, trademarks can remain in force potentially forever.

The iPod shape trademark gives Apple a new weapon in the fiercely competitive market for media players. While competitors may eventually appropriate the iPod's inner workings, as utility patents expire, they will risk litigation if their products come too close to the trademarked shape of the iPod, including its popular circular-touchpad interface.