Occasionally your mailers may arrive with a barcode on them. The barcode generally means that for some reason, USPS was not able to use the barcode in the address block for delivery, so they applied this new orange barcode by reading the name and address for delivery. It should only be on pieces that either do not contain a full 11 digit delivery barcode or an incorrect delivery barcode.
USPS reserves the right to spray the additional orange barcode for certain locations for internal purposes to accommodate machinery needs, so sometimes they spray it to accommodate their equipment or lack of.
You can read more about this here.