wwII japanese Parker w/ pics

[Tom Greene]

My father recently passed away. He has a Parker shotgun that was given to him by his cousin who was with the initial american forces that entered Tokyo towards the end of wwII. He told my father that the parker was used by the Japanese millitary in a prisoner of war camp. The buttstock is stamped with a 4 digit "inventory" # preceded by a Japanese symbol/marking. Have any of you heard of such? Any info will be greatly appreciated. The serial number is 220053 and on top of the sight rail it reads "Parker Bros makers Meriden Ct usa vulcan steel"