You did get a sweet deal, I've never seen one shaped like that. Looks like a cigar mold.
Apparently it's not rare at all. But I did find out there are 15 variations of this particular cornbread pan and this is variation no 12. Here is a picture of it cleaned up and getting the first round of seasoning with some of its siblings.
From top left going clockwise:
Griswold Cornbread pan, vintage lodge skillet, Griswold no 5 skillet, unmarked square skillet, bacon press, BSR Skillet