Section 128(2) in The Bihar Motor Vehicles Rules, 1992
(2)A transport vehicle when regularly used for carrying Government mail by or under a contract with the Indian Posts and Telegraphs Department, shall be painted in postal red colour and shall exhibit in a conspicuous place upon a plate or on a plain surface of the motor vehicle the word "MAIL" in red colour on a white ground, each letter being not less than 15 centimeters in height and of a uniform thickness of 20 millimetres.
