Like Doc Hoy, I have seen kit guns with that ring. The barrel is one piece, the ring is the result of just leaving the barrel partly finished.
IIRC, Italy does not proof test or require manufacturer's markings on parts, only on completed guns, so I suspect that comments about its Italian origin are correct. The bluing appears to be cold blue.
That does not mean the gun is bad, or dangerous, and is no reason not to buy at the right price if everything seems to work OK.