Since this is a "GUESS" post suppose we all could theorize most anything. There were several skillets that had three notches placed at 120 degrees apart but they also had straight raised lines leading toward the center of the skillet and also an outer raised heat ring with breaks where the raised lines lead inward. Some collectors labeled this type skillet as the "Mercedes Skillet" simply because it takes the appearance of the Mercedes Benze auto-maker. Besides the proclaimed BSR skillet, Wagner/GHC made a similar skillet shown on P. 235 of the BB except the handle design was different to the regular skillets.
Again...just a "GUESS", but think a local foundry (or someone experimenting with cast iron design). used a Wagner skillet as a base skillet and incorporated the 120 degree break in the heat and are probably laughing at all of us trying to I.D. something that was never produced by a major company dealing in C.I. products.
I come across some of these oddities from time to time and if they are of good quality I will clean and season them and re-sale without any proclamations as to maker.