The Universal Product Code, or UPC, is a code used by manufacturers in many countries on saleable items. Since most UPC symbols are unique to the product line they are displayed on, they can be used for everything from inventory tracking to price scanning.
UPCs are almost always located on the manufacturer's box and looks like a series of black bars of various thicknesses, also called a bar code. Below these bars is a 12 to 14 digit series of numbers.
Many companies treat these as the proof of purchase as items are generally considered un-sellable and unable to be returned once they are removed.