XML co-inventor and Android Developer Advocate Tim Bray is submitting a draft for a new HTTP Status Code to be used when resources aren’t available because of legal restrictions. The code, 451 Unavailable for Legal Reasons, could be used to let users know that the web page or resource they are requesting can’t be accessed because of state censorship, for example. Internet Drafts aren't standards, but ideas that may end up being standardized by the IETF down the road. According to the 451 draft, responses using the code should indicate details about the pertinent legal restriction, which legal authority is behind it, and what class of resources the restriction applies to.
Since the UK High Court ordered UK ISPs to block The Pirate Bay, some have taken to using the 403 Forbidden status code to indicate the site is unavailable. However, a blog post by Terence Eden points out that 403s are meant to be used when "the server understood the request, but is refusing to fulfill it." When an ISP blocks access to a site like The Pirate Bay, the server never sees the request, which makes the use of a 403 code technically inappropriate. As Bray notes in the draft, use of the proposed 451 code is optional, and "it is imaginable that certain legal authorities may wish to avoid transparency, and not only forbid access to certain resources, but also disclosure that the restriction exists."