If I remember correctly, those weren't stamped but embossed.
Something stamped to me would have a negative space on the flight plate. (ie. something hot pushing into the plastic). Most of the titanium plastic of that era the 'artwork' was raised off the flight plate.
That's correct, it was a "negative" stamp, I never knew how they really did it because it was raised and that seems way more difficult to pull off correctly than stamping into the flight plate.