Amid concerns about crime and public safety, at least two major U.S. cities recently considered banning ski masks or balaclavas to prevent criminal behavior, despite a lack of academic research about the effectiveness of such bans. Last month, Philadelphia became the latest city to enact a ban in some public spaces, including parks, schools, day care centers, city-owned buildings and public transit. The ban comes with exceptions for working in cold weather, religious expression and activities such as protesting and playing winter sports. The ban, introduced last June, came after a series of fa…