TheStreet's Jim Cramer says the transports have always been the most important index he follows. Cramer says transports have been going higher recently, unlike airlines and railroads. Packaging, too has been going up. Cramer points out that UPS reported a bad number and the stock dropped from $100 to the low-$90s. However, the stock is now back over $100 because retail sales are doing better and the harsh winter weather is over. Cramer regards UPS as the tell that the tepid April retail sales number is going to be wrong. Cramer likes retailers going into earnings because UPS is telling him that shopping is back.