My understanding is that the emblem was ground off surrendered weapons at the end of WW2, likely by order of Gen McArthur. The royal chrysanthemum was the symbol of the Imperial Family, and was ground off by either US troops/Japanese to save face, handing over a rifle with the chrysanthemum intact was considered a 'dishonour' to the emperor. Rifles with them intact are generally accepted to be battlefield pickups.
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