Sorry, I wasn't thinking when I asked about the step but obviously, if the grips needed to be removed to see the serial, the gun would not be a Regulation Police.
If anyone has a standard (not RP) I frame with the number on the front of the grip, can you post pictures? AFAIK, only the RP had the serial number on the front strap, the reason being that the standard RP grip covered the butt. But on other guns, the serial was on the butt. While some grip styles covered the number, it would not be known until final assembly what grip would be installed, long after the serial was put on.