Going back to the subway metaphor: if you by your NYC metrocard with a credit card, the police can (and do) track you. There have been incidents with people bei

Going back to the subway metaphor: if you by your NYC metrocard with a credit card, the police can (and do) track you. There have been incidents with people being charged with---and exonerated from---crimes on the basis of their travel logs. I can't find the citation currently, sorry.