Earlier this month Google developer advocate Tim Bray proposed a new HTTP Error status code aimed at shining a light on web censorship.
Bray’s new Error 451 would work somewhat like the Error 404 pages you’ve probably seen. But instead of telling you that the page could not be found, an Error 451 response would let you know that the page you were looking for had been censored.
As it stands, most web-blocking tools return a 403 error (which means access is forbidden) when denying access to censored pages. For instance, UK ISPs, which are now required to block The Pirate Bay, typically return a 403 error code when doing so — via redwolf.newsvine.com