丹书铁券

Explanation: Dan Book: The cinnabar write; iron Lease: The iron's certificate. Hero of the ancient emperors for generations to enjoy the preferential treatment given or a certificate of impunity. Diploma in Writing by Dan on iron, hence the name. 　　Source: "Biography of the Later Han Ji Compliance": "Dan Book Rail tickets pass to infinity. 　　Examples: North Korea first give a ~, live and work. (Qing Chen Chen, "Water Margin after the transfer," the twenty-seventh back)