Has anyone ever seen this? I did confirm that this is not zinc rusting through or a bubble etc. The D is rotated to the right. I can't find anything on a 1971 D error though. http://www.flickr.com/photos/mitchelliii/4809739656/sizes/o/ http://www.flickr.com/photos/mitchelliii/4809738910/sizes/o/in/photostream/ Cheers.
From the pics, it looks like damage, probably whatever hit the top of the "7" also hit the mint mark.
Mint Marks were applied by hand in 1971 and their position and orientation can vary quite a bit from die to die.