Briefly, Subway demanded a local hot dog restaurant, Coney Island Drive Inn (whose website is http://www.gotfootlongs.com) stop using the word "Footlong" to sell its foot long hot dogs. Since Coney Island Drive Inn has been selling footlong hot dogs since 1963, the restaurant was surprised by Subway's demand.
Subway is still negotiating with the U.S. Patent and Trademark Office in its attempt to get a trademark registration for the mark Footlong. Subway's trademark application was initially refused for being descriptive -- "Footlong" merely describes a feature of applicant's goods.
Subway responded by arguing that the mark had acquired secondary meaning -- the consuming public has grown to associate the mark "Footlong" with Subway's services. To support this argument, Subway provided evidence that it had sold almost 1 billion (yes, with a "b") sandwiches in 2008.
The Trademark Examining attorney retracted the distinctiveness rejection (agreeing that Subway had put forth evidence of secondary meaning). But Subway and the Patent and Trademark Office are continuing to argue over whether or not Subway has shown use of the Footlong mark in connection with "restaurant services," the goods/services Subway claims it has been using the mark with.
The file history of the negotiation between Subway and the Patent and Trademark Office is below. Since all the attention from this cease-and-desist, Subway has since retracted the demand, stating it was a clerical error and it should not have been sent to Coney Island Drive Inn in the first place.