Paul Greaves was kind enough to point me in the right direction :

When an S.F. blot starts to wear, only the embossing should show through ( just the S.F. in a 102 star's case) These show missing mold material all around the area just above star.

I had believed at one point, that in just the right light I had seen an "S.F." in there. (-quite honestly I was looking for anything but an S.F., as it would be more interesting.) I'm sure if I stared at it long enough I could see whatever I wanted in there, but:

There are no S.F. 102s in this profile, -or with the embossing that high up on the skirt.

Appears to be corrosion... oxidation, OXIDES!! on mold, pitting of the mold surface that results in bumps, mounds, globs, whatever you want to call it of 'extra' glass on surface of insulator.

Thanks again to Paul!