"ATI AIB (1787)", whatever that means.
Basically a generic ID for those cards using a stock AMD BIOS, as I understand it. Hovering over the field would show that it could be PowerColor, HIS, and I'm finding XFX mentioned in some searches.
Serial number stickers on the PCB gone, too? Really stupid if that's the case. Could probably be identified visually unless it has the generic black shroud w/60mm fan covering the whole front of the card. Beyond that you might find some characters etched on the PCB, but that might even require removing the cooler.
Not much to be had outside of academic curiosity at this point. You likely won't find any specialized software or drivers for it and the entire 5xxx lineup was retired to legacy status a few months ago.