[Help] on the serial number format USB-I2C problem

busLab

Previously bought a few test machine when the serial number is 12-bit string "0 BU7421" and the like, some non-AscII characters.
So my host program in the middle of the first 4 to 10 out stored in the database.
now buy 50 found when looking at numbers 4 through 10 are not insurance, there are non-ASCII characters or symbols go in.
Q. What are the specifications this number yet?
support rewrite it?
able to turn into all ASCII characters?
Or else more troublesome ah.