If they are impressions, they cannot be from time of molding unless they were tiny hemispherical pieces placed on the surface of the mold cavity, which is highly doubtful, if even possible to have remain in place as molten iron flowed in. So, they would either have to be in the pattern, also doubtful, or added to the pan itself, probably with a small high speed drill bit. Perhaps a previous owner wanted to mark it in some casual way to identify it if it got "borrowed".
Sulfur pitting and collectible condition aren't compatible terms to me. That's not even a $20 skillet on a good day. The only reason I have one just like it is because it belonged to my grandmother.