A web-wide system isn't feasible. A websites respect for your privacy is an issue of trust and not something you can easily quantify. For example, DuckDuckGo pr

A web-wide system isn't feasible. A websites respect for your privacy is an issue of trust and not something you can easily quantify. For example, DuckDuckGo promises not to track you (and I believe they don't) but proving this claim is impossible without access to the server.