Pardon my ignorance, but I am trying to determine the meaning of a second line below the serial number of a Colt M1860 Army revolver. This particular Colt has a serial number of 49136, but on a line just below the serial number is the number 2, see photo. All the serial numbers match, but all have the number 2 stamped just below. Can someone tell me what the number 2 indicates? Thanks for the help.