I'm far from an Arisaka expert but those circles are where the imperial Chrysanthemum ("Mum" for short) should be, or possibly was...
After the war, with Japan occupied, many (if not most) of the surrendered rifles had the Mum removed/scrubbed, or otherwise defaced. Stories vary, some say the Japanese did it, so they would not be surrendering the Emperor's property, some say the Americans did it, to give the Japanese a way to "save face" and promote their compliance and co-operation. I have no clue which is true, either could be, or both could be.
All I know for sure is that the rifles surrendered at the end of the war had the Mum's "ground" and while there probably are exceptions, the majority were scrubbed of the Mum and Arisakas that still have the Mum intact are generally assumed to have been battlefield trophies, not rifles surrendered at the end of the war.
No idea what the circles mean only that they are in the location where the Mum would have been on a service rifle.
The though occurs to me that the circles MIGHT be the start of the Mum marking, which was never completed on that rifle.
