Generally it is printed on a white or some other color label/Sticker which is glued to the GPU PCB board or it is printed right on the PCB Board itself.
From Powercolor Warranty site: https://www.powercolor.com/rmaus
An easy way to identify whether or not your product is “refurbished” or not is to examine the Serial Number sticker (S/N) on the back of your VGA card.
Removal and/or damaging of serial number sticker(s) on the back of the product will VOID all warranties.
Found this YouTube video showing the S/N Sticker location on the Powercolor RX 7900XTX: https://www.youtube.com/watch?v=zmRt1PYrIu8
