Every so often I buy what appear to be completely worthless lots of common German stamps on
ebay in the hope that the lot will yield something interesting. That strategy seems to have paid off, for this is only the second inverted overprint I've ever found. It's Occupied Germany (1948), 10pf with posthorn overprint (Michel 54 I).

This variety is not listed in my Michel (I haven't looked at Scott yet). I'm pretty sure it isn't common, so if anyone has a Michel Specialised Volume II, I'd really like to know what they list it for.