I brought up this question because I was in our factory last week and noticed
the "ID:" field on our labels was empty. In fact it was my mistake, the first
batch of Ben NanoNotes will not have serial numbers (but at least we know all
NanoNotes without IDs are from the first batch). When they offered to engrave
the plastic with a laser printer I felt even more like this should better be
thought through.
So thanks for the many different reactions we got here!

In the beagle boards we have a small glued on lable with the distributor ID and serial number. Easily removable by the consumer from the board but can be noted and kept for filing bug reports and RMA.