Jeff sez: '...The lettering we see on 2-2-V-1 is likely due to weathering where visible ink once was - or more precisely, perhaps to weathering of the surfaces around where the visible lettering was. It seems that even with the visible ink polished off there may remain enough trace to produce this result."
Jeff has described a process I have some experience with - Lithography, printed-circuit-board fabrication, and sand-blasting all make use of a "resist" coating that only covers the areas that you don't want etched. The resist is a sort of paint, more resistant to the etchant than the exposed metal. Removing the resist after etching leaves the desired pattern. Something similar may have happened to 2-2-V-1, in which the printed label resisted erosion while the exposed metal got etched. Sand abrasion seems like a likely process, considering the environment it was found in. This isn't to say there would be any ink or paint left, the printed areas are simply the last to be exposed, leaving a ghost image that is simply a different surface texture that the area next to it. The resulting ghost image may only be visible under specific lighting conditions, but may also be made visible by wetting the surface. Visit a print shop that uses offset printing to see how it's done, and what the plates look like before they're inked.