サイト名は HTTP/1.1 ステータスコードからとりました。404 Not Found で Google 検索 してみると予想通りの結果だったので、少し捻って 204 No Content です。

The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.

If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without
causing a change to the user agent’s active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent’s active view.

The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.

Quotation from urn:ietf:RFC-2616 10.2.5 204 No Content