Some while ago there was a topic on odd serial numbers. I just remembered to look at the back of a particalar HP48GX of mine for the codes. Randy asked about them, so I'll list them here:
There is a white sticker with the official HP logo and in bold letters the phrase: WARRANTY VOID IF REMOVE. Underneath this was the following serial number: S/N: 3537S00447
There is also a white sticker with a barcode and the following number underneath this barcode: 7500Z1005
Now, none of these numbers match up with the serial number that is normally found on the back of an HP48 near the nameplate area: ID15001197
Again, my original theory was that this calculator was a replacement unit for the one with the serial number 3537S0047. Perhaps that is why that sticker is there with WARRANTY VOID IF REMOVED. But at this point, the only replacement units were the black-LCD Indonesian models... maybe?
I'll add a photo once my laptop is back up and running (using the forum via the university computers at the moment).