Ithaca 37 stock markings?

[falcon]

At a gun show the other day and bought this 1970 parkerized Ithaca 37-with 20" barrel, off of a walk-in.
Stock markings have U.S.N , 67+mushroom stamp and U.S. + mushroom stamp underneath stock grip/cap area.
Has any one seen these stamped style martial (US/USN with mushroom) markings before? Was thinking some previous owner may have added them to make it look like it was used in military service but I'm not so sure.

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