Section 251(2) in The West Bengal Motor Vehicles Rules, 1989
(2)A public service when regularly used for carrying Government Mail, by or under a contract, with the Indian Posts and Telegraphs Department, may exhibit in a conspicuous place upon a plate or a plane surface of the motor vehicle, the words "Mail" in red colour on a white ground, each letter, being not less than 15 centimetres in height and of a uniform thickness of three-quarters or 2.5 centimetres.
