It kind of looks like there was something stamped there, but was worn off over time. Take a magnifying glass to it, and see if there any remnants of letters. And it looks like the Peterson name was wiped off the band above the K&P shield. Was it?
I agree it's a rocky Donegal, and Peterson stampings often don't go far into the the briar. I do see faint remnants on the back that I tried to read with a magnifying glass with little success. Maybe @scottb will have better luck with the pipe in hand and will post a clearer photo of it. I'm wondering why the name "Peterson" is blanked out on the band. Maybe @ashdigger has a thought or two on this?i do have a 1979 Doney rocky xl 02 and rustication looks similar and I also have worn out stampings on the flat spot.