There's a 1930 Dante Rancilio C-mel for sale on ePay now, Hadamard:Yes, a mysterious curved C soprano!
The research didn't led too far, but it seems like Rampone produced it and Rancilio put his name on the bell.
I only found evidence of three of such beasts on the Internet...
Looking into it, I found a 2005 article, "Saxophone Manufacture in Italy: A Short Survey," by Emanuele Raganato, who suggests that D. Rancilio produced their own horns from 1914 until WWII. So maybe your curved C soprano isn't a Rampone stencil after all, but a true Rancilio?