I had an NID 12 ga. 26" that had the Ithaca factory markings on the reciever, but no marking on the barrels. And no serial numbers, nor any sign it ever had them*. Bought it at a small gun show about 40 miles from Ithaca. Guess where that came from?
(*I occasionally watch cop shows and am always amused by the "the serial numbers were filed off" line, especially on tiny S&W snubbies and Raven .25s. SOMEBODY out there in criminal land is a MASTER filer.....and what's left of the gun when the Master is done?)