the number at the back in the circle is 270 I think.
I assume here you are speaking of the elongated C. If you examine it real close it probaly reads 12-70. The C stands for chamber & then gives the gauge & length of shell for which it is chambered.
The Lefever Nitro Special was built in the US by Ithaca. The US has never had an official proof law so no "Proof Marks" will be found. It would have been proof fired in-house by Ithaca. I don't currently have one so don't recall how or if they were marked to state that.
