"Black Friday" as a term has been used in multiple contexts, going back to the 19th century[31], where in the United States it was associated with a financial crisis of 1869. The earliest known use of "Black Friday" to refer to shopping on the day after Thanksgiving was made in a public relations newsletter from 1961 that is clear on the negative implications of the name and its origin in Philadelphia:
For downtown merchants throughout the nation, the biggest shopping days normally are the two following Thanksgiving Day. Resulting traffic jams are an irksome problem to the police and, in Philadelphia, it became customary for officers to refer to the post-Thanksgiving days as Black Friday and Black Saturday. Hardly a stimulus for good business, the problem was discussed by the merchants with their Deputy City Representative, Abe S. Rosen, one of the country's most experienced municipal PR executives. He recommended adoption of a positive approach which would convert Black Friday and Black Saturday to Big Friday and Big Saturday
http://en.wikipedia.org/wiki/Black_Friday_(shopping)#Origin_of_the_term