Section 165(2) in The Punjab Motor Vehicles Rules, 1989
(2)A public service vehicle, when regularly used for carrying Government mail by or under a contract with the Indian Posts and Telegraphs Department shall exhibit in a conspicuous place upon a plate or a plane surface of the vehicle the words 'MAIL' in read on the white ground, each letter being not less than 100 milimetres in height and of a uniform thickness of 20 milimetres.
