Could it be that there was a general consensus that 350 & 370 model # was an indication of the displacement and that calling it the 400Z would be misleading? So IV is #4. Mystery solved.
Didn't notice this until I saw your post. My G37 had the same mirror, but I never noticed his marking there, and that car is long gone now. I think @takemorepills may still have a G37. Maybe other 370Z owners can chime in.
My 2024 Nismo has it. I never noticed until I just looked.
I asked Google, and not sure if it's just made up AI stuff, but here is the response:
The "IV" Roman numeral on a Nissan Z typically signifies the "fourth generation" of the Z car model line, as "IV" represents the number 4 in Roman numerals; meaning your Nissan Z belongs to the fourth generation of the Z car series.
Key points to remember:
Roman numeral system: "IV" is the Roman numeral for "4".
Generation indicator: In car design, using Roman numerals often indicates the generation of a specific model.
Nissan Z context: On a Nissan Z, the "IV" signifies that it belongs to the fourth generation of the Z car line.
Most likely a manufacturer or certification marking.
OEM pn 999L1-VZ001 is the rear view mirror for 2016-2019 Pathfinders, Rogues and Sentras, and it has that identical “IV” laser mark.