To every vehicle conforming to a vehicle type approved under this Regulation there shall be affixed, conspicuously and in a readily accessible place specified in the Annex to the type approval certificate shown in Annex X, a symbol being a rectangle surrounding a figure expressing in m-1 the corrected absorption coefficient obtained, at the time of approval, during the test under free acceleration, and determined at the time of approval by the method described in item 3.2 of Annex IV.