Apple is taking a page from Napster and XM, using the new HD Radio service to debut a new feature called "iTunes Tagging."

Consumers with HD Radio receivers with a special tagging button would be able to mark songs for download from Apple's iTunes Music Store. Although it's not clear how exactly a user's tags would make it to iTunes, JBL and Polk would be the first to produce devices.

A similar offering from Napster and XM allows specially-equipped receivers to mark songs as they are played, with the selections transferred to the Napster Music Store when that receiver is synced with the user's computer.

The iTunes Tagging idea came together rather quickly, and is a joint effort between Apple, iBiquity Digital, and several broadcasting groups including Clear Channel. An exact number of stations to initially participate was not available, although press materials said it numbered in the "hundreds."

"Research consistently shows that radio is the predominant source of music discovery," iBiquity CEO Bob Struble said. "We are especially pleased that so many broadcasters came together so quickly for the initial launch."

A more formal announcement of participants is set to be made during the annual convention of the National Association of Broadcasters, to be held September 26-28.

Initially, products with the tag button would be aimed at the home, but Struble said by early 2008 products would begin to appear for the vehicle as well. The first products to have the button would be the new Polk I-Sonic Entertainment System 2 and the JBL iHD.

"Several hundred thousand" HD radio receivers have been sold since the launch of the format in 2005, according to iBiquity.