>>11382622
adding onto my post >>11382598 because slave registries are living institutions, they may change within the lifetime of a slave, so it's important that the slave's unique identifier not be tied to any arbitrary numbering scheme that can't be carried over to a successor slave registry. this is the biggest advantage to using something like UUID for lifetime identification of the slave, since there's a 340 billion billion billion billion possible UUIDs and they're commonly used.
but for the same reason you'd want a UUID for lifetime identification, the registry could give a shorter number (or even a personalized / requested number) for everyday reference to a particular slave registered there. they don't have to be unique outside of the registry.
UUID is like a VIN, and the shorter number (i guess call it a registration number) is more like a license plate. UUID is long, unique and definitive. Registration number is easier to remember and write down.

separately to note, the old U.S. postal barcodes (POSTNET, PLANET) are very easy to draw on skin with nothing but a ruler and a marker. take note if your budget is low or you are long distance with your sub