According to the Badger and Blade, the numbers on the edge of a double-edge razor are for the manufacturer's quality control. Some appear in Roman numerals, and some in standard numbers, but some may not display any numbers at all.
The numbers on a double-edge blade are not for direction. The numbers have no bearing on what side is put in first or which is the top side and which is the bottom side. Double-edge blades can be put in either way, and the numbers are solely for use by the manufacturers in their own testing and in-house quality control.