Tin Plate with a differential coating has a continuous mark all the way through one of the coil longitudinal faces (like wise on all sheets) thereby identifying heavier coated side.
Characteristic mark will be applied in accordance with sequence in which the order was specified.
If the order specification say D 5.6 / 2.8 gm/m2, the mark is applied on more heavily coated side as per the figure representing the 5.6 gm/m2 value.
If the order specified D 2.8 / 5.6 gm/m2 the mark is applied on the side with lighter coating.