Type 38 Carbine Marking

I recently purchased this Nagoya Type 38 Carbine 5th Series. I noticed a marking on the receiver tang, a round stamp. Does anyone know what his may be? This carbine was imported.
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If it’s import stamped, I assume it is a Chinese capture rifle and the stamp signifies it’s been inspected or reworked…maybe a unit marking but too worn to make out. Is it still in 6.5 or converted to 7.62x39 or 8mm?