If it's a little grey tag, and says "Serie Parti Meccanichi" (Mechanical Part Number) it is the engine number.
My motor number is 4392 (my VIN is 5357).
You will find this same number stamped on the rear of the engine block. It is up towards the top, between the drivers side head, and the ZF Bell Housing.
Let me know if this is what you are seeing.
Regards -
Rocky
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