Alan Greenspan was fond of tracking liner board prices. The idea is simple: liner board is a main component of cardboard, which is used as packaging to ship just about everything. When liner board prices surge it means that packaging is in demand, which can only be the case if people are buying things, which in turn signals a healthy economy. Demand of a sort is already ticking higher: alleged financial criminals like Bernie Madoff using the stuff to cover their car window on the way to court. But cardboard is in a deadly bear market. Prices for the raw material used to make boxes are in freefall, having hit $25 a ton in January from $115 in September, according to Mark Arzoumanian, Editor-in-Chief at Official Board Markets. When the price turns up it will mean people are shopping again. Liner board isn't easy to track. As a proxy, keep your eye on the stock price of leading cardboard producers Smurfit-Stone Container Corp. (ticker: SSCC) and International Paper (IP). Their shares began falling before the recession started and could turn higher before the recovery begins.