Shortly after the breakup of Conrail, letters (A.K.A. reporting marks) of the new owner were applied to Conrail units below the number on the side of each locomotive unit. Whereas CSXT used those initials only, NS elected to research who the engine was from and apply those initials. Even before that, NS would apply the initials of the former road below the number, even when painted in their paint scheme. Example would be CNOTP, but for movement purposes, it would be identifed as NS. Another is CG for the Central of Georgia. Back to the days shortly after Conrail, when these units wandered out, crews would see them painted in Conrail and, for movement purposes, would want to identify them as such. Not so! They had to look for the initials below the number on the side of the cab. Heneforth, this instruction that you have seen. NS's new Heritage Painted Units have nothing to do with it.