Section 186(2) in The Bihar Motor Vehicles Rules, 1992
(2)The mark shall be kept clean and unobscured and shall be so fixed to the trailer that-(i)the letter on mark is vertical and easily distinguishable from the rear of the trailer,(ii)the mark is either on the centre or to the right hand side or the back of the trailer, and(iii)no part thereof is at a height exceeding 120 centimeters from the ground.Chapter-VIII Control of Traffic
