The short answer is that during the final polish step, the obverse was not held to the wheel quite long enough.

The longer answer:

During the many steps to forge and finish the blade, the last two were:

1. Apply the darkening agent (called "burnishing" in the hobby. This was NOT done by painstakingly using a fine paintbrush to fill in the letters of the motto and trademark. There was not the time.

It was done with some sort of small swab. One sweep down the motto, filling the letters and the adjacent higher points with an indelible darkening agent. One smaller hit on the back to fill in the trademark. Or, a long sweep if it is a dagger with the Rohm or Himmler inscription. At this point the motto and surrounding area looks like one black or dark grey band about 1 cm in width. The trademark is a dark blob.

2. Final grind or polish. The blade was held against the wheel to make it look attractive. It ground a very thin layer of steel from the blade. In doing so, it ground off the darkening agent off the high parts of the motto/trademark, leaving the motto and trademark with a beautiful dark contrasting look. Every now and then, the worker took the blade off the wheel a second too soon.

That is when you see spidering.

Dave