Those tiny stickers on loose fruits and vegetables at the market have a worthy purpose. Besides telling the store's computer database at checkout what the item is and how much it costs, the price lookup code (PLU) tells you how it was grown. Conventionally grown produce carries a four-digit code. On organically grown items, a number 9 precedes that basic code, on genetically modified produce a number 8. The number on a conventionally grown apple, for instance, might be 4133; on an organic apple, 94133; and on a genetically modified one, 84133.