You see HTTP status codes all over: "404 Not Found" for mistyped URLs, "403 Forbidden" for authorization failures and traffic problems read as "503 Service Unavailable". We may now need a new one for legal restrictions, and what could be more fitting than "451" in honor of Ray Bradbury?
The number "451," of course, refers to Ray Bradbury's novel Fahrenheit 451. Specifically, 451 degrees Fahrenheit is the approximate temperature at which paper ignites, and there's a lot of igniting of paper in the novel, which is all about a hypothetical future where books are banned and burned by government dudes with flamethrowers when found. As such, it would be a rather appropriate HTTP status code for those times when a website has been made inaccessible for legal reasons.
This isn't just a silly idea that's being kicked around to draw attention to Internet censorship or something like that. At the moment, websites that have been legally blocked return status code "403 Forbidden," which is not accurate. The 403 code means that the server (the website itself) is refusing you access, when it's actually your ISP or the government or some other authority that's jumping in the middle and keeping you from your data. A 451 code ("451 Unavailable for Legal Reasons") would make it clear that it's not your computer, or the website, but censorship somewhere in between.
The 451 error code proposal, which was first conceived of by Tim Bray, will be discussed at the next meeting of the Internet Engineering Task Force next month. If it's approved, it'll be fairly fast and easy to deploy, but only as an optional status code: any legal authorities who want to avoid disclosing that they're censoring will still be able to censor the 451 status page itself, and instead send you to an inaccurate 403 page. Sigh. Maybe the best solution really is to just nuke society and start over from scratch.