Arvind Narayanan discusses how the “Do Not Track” concept can be applied using a header-based approach that would signal web sites not to track:
…. Today, consensus has been emerging around a far simpler DNT mechanism: have the browser signal to websites the user’s wish to opt out of tracking, specifially, via a HTTP header, such as “X-Do-Not-Track”. The header is sent out with every web request — this includes the page the user wishes to view, as well as each of the objects and scripts embedded within the page, including ads and trackers. It is trivial to implement in the web browser — indeed, there is already a Firefox add-on that implements a such a header.
The header-based approach also has the advantage of requiring no centralization or persistence. But in order for it to be meaningful, advertisers will have to respect the user’s preference not to be tracked. How would this be enforced? There is a spectrum of possibilities, ranging from self-regulation via the Network Advertising Initiative, to supervised self-regulation or “co-regulation,” to direct regulation.
Read more on 33 Bits of Entropy.