Any idea what brand CI this is?
There was a period in which any decent foundry could make CI skillets, and sell them as generic, no name, items in hardware and department stores. The numbers are standardized sizes.
Check out this site:
Also, the folks who collect Griswold and Wagner have a wealth of info on old cast iron.
PaulJ is right...there used to be a lot of small foundries casting skillets. There was also a lot of cast iron made by bigger foundries like Lodge, Wapak, Griswold and Wagner that is unmarked...it was product that was marketed by department stores and the like. Suffice to say, lots of old cast iron is hard to trace. This doesn't help if you are a collector. If the condition of the pan is decent, it should cook just fine, and makes a lovely conversation piece if nothing else. Some of those pans have a lovely unique appearance and are worth hanging onto.