Should cryptocurrency be a reward, if not a means of payment? In the United States, fast food chains are seriously testing the waters to analyze how they should integrate bitcoin, dogecoin or other cryptocurrencies into their business models. The latest initiative comes from Shake Shack, which is running a promotion awarding the equivalent of 15% of an order back in bitcoin to customers who pay using a mobile payment service. Would you be tempted to buy a burger if it promised to grow your cryptocurrency savings? In the United States, Shake Shack restaurants have chosen bitcoin to test whether…