Jeff, as a general rule of thumb, if the town doesn't have any rules or regulations that prohibit metal detecting it is usually okay. The only thing I would question though is if the common that you were detecting is a historic site or on the national registry, then someone might complain. Similar to Tom in CA's thoughts, If you go to the town hall you might wind up talking with a bureaucrat that isn't a fan of MDing. You could always go when she's not around.