Section 71(5)(b) in Delhi Motor Vehicles Rules, 1993
(b)the permit number in addition to the registration mark shall be painted on the cab in white in a red circle, the six of number being 5 centimeters in height and 4 centimeters in breadth at four different places:(i)on left hand top portion of the windscreen readable from inside,(ii)on the rear boot against the black background.(iii)on the left front door against black background,(iv)on the right front door against black background.