Early in the manufacturing process frames are fitted with yokes and side plates then those three parts are stamped with an assembly number to keep them together. Serial numbers are assigned later. 32187 is your .22 Combat Masterpiece's assembly number. It will also be on the left side of the grip frame and back side of the side plate.
With no apology to owners of .22 Diamond Backs, .22 Combat Masterpiece's were the classiest .22 revolvers ever made.