Seems to me, the reason we have marked police cars is that part of their crime prevention strategy is to maintain a high degree of visibility. Were this not the case, all cars would be unmarked. This app then simply expands that visibility so you can know that big brother's little brother is watching. I am assuming most unmarked cars will not show up in this app, so that tool is still available to law enforcement. Plus, as a criminal, are you really going to trust the cell-phone-wielding masses to catch them all?