Some tags are obvious, such as those used for E-Z Pass toll collection on northeastern U.S. highways;others are more insidious, such as those tucked inside U.

• 有些标签显而易见，例如美国东北区高速公路使用的电子收费器，其他的就比较隐密，例如藏在美国护照和伦敦地铁旅游卡中的标签。