According to the Digital Watermarking Alliance:
Digital watermarking can enable content identification and copyright communication on a broad scale and can provide a range of solutions for identifying, securing, managing and tracking digital images, audio, video, and printed materials. These industries use digital watermarking to identify, protect and manage the rights to their content as they embrace innovative distribution or business models and provide consumers with new entertainment experiences, enhanced convenience, and greater portability of their media content.So far, record labels have mostly been using watermarking technology to discourage reviewers from leaking advance copies of discs on the internet. Of course the watermark only works if this way if the person who was originally given the disc is the one who leaks it, as this story about a label calling out an 'innocent' reviewer illustrates.
But watermarking could be the next DRM as the industry continues to look for ways to monetize digital content delivery and limit illegal file sharing.