Spirit Airlines is a major economic force in South Florida: it is the second largest carrier at Fort Lauderdale-Hollywood International Airport; it is a top five employer in Broward County with more than 3,000 regional employees; and it is one of the largest South Florida companies with more than $2.5 billion in annual revenue. But you wouldn’t know this by its headquarters in Miramar. It’s tucked away in a light industrial neighborhood of low-slung office buildings. There is no grand sign