Snopes.com confirms here that the Subway sub club was done in by counterfeiters:
"Ever since the 1980s, Subway customers have received a stamp for every six-inch sandwich purchased (two stamps for a foot-long); filling up a Sub Club card with the requisite number of stamps entitles the customer to a free sandwich. Alas, by the end of September 2005 the Sub Club will be no more, another victim of technology which makes counterfeiting coupons and proof-of-purchase stamps on home computer equipment all too easy."
The first Subway I ever went to was run by some Vietnamese people in Cherrydale in Arlington and I thought it was such a novel and fantastic idea. Now, Abingdon has three of them.