From Comp.sys.hp48, a post by Joe Horn:
"GOOD NEWS! HP recently started putting the hp49g+ serial number on the
*outside* of the plastic packaging!
It's on the back side, near the top, next to the hole that's used for
hanging the package from a peg in the shop. I uploaded a photo of one
such serial number here:
http://holyjoe.net/hp/sticker.jpg
It's a silver-colored sticker with black printing, same as the
calculator's *case* serial number, but slightly different (of course)
from the boot-sector serial number which is returned by the SERIAL
command (if typing SERIAL doesn't work, type 256 ATTACH and then try
again).
There are a few other differences I've seen between my original hp49g+
and this new one, most notably FLAWLESS keyboard response (so far!
hooray!!!), nice tactile feel, and nice click.
-Joe-"