Gents,

Thanks for all of the input! This is exactly why this BB is such a superb venue for the exchange of information. It would have taken me years to get to the bottom of this otherwise.

Here is a macro of the action which shows more detail. Click on the picture and enlarge it for more detail. I took a few images and this was the one which shows the lines the best. If you look closely, the lines do not appear to be scratches as scratches would drag some metal into the engraving in the direction of the scratch (or so I think).
I think the lines show some personality on the old girl and I'm glad to know that these are natural and not some external damage to the gun.