Source: Shutterstock A shopping cart full of bargains might be telling Wall Street something a designer handbag cannot. Walmart has been outperforming luxury retailers in the stock market, and investors are paying attention. Normally, that sounds like a straightforward success story for America’s biggest retailer. But longtime investment strategist Jim Paulsen sees another possibility: households may be becoming more careful with their money. His unusual economic warning system helps explain why a discount retailer’s winning streak could signal trouble elsewhere.