Read HTTP 451 (en.wikipedia.org)

In computer networking, HTTP 451 Unavailable For Legal Reasons is an error status code of the HTTP protocol to be displayed when the user requests a resource which cannot be served for legal reasons, such as a web page censored by a government. The number 451 is a reference to Ray Bradbury's 1953 dystopian novel Fahrenheit 451, in which books are outlawed.[2] 451 intends to provide more information than 403 Forbidden, which is often used for the same purpose.[3] This status code is standardized in RFC 7725.

I love that it’s a subtle nod to Fahrenheit 451.