User blog comment:ImperiexSeed/Supernatural Mysteries/@comment-6449959-20130212215814/@comment-3481504-20130213212058

No one, but God, can hid who/what they are. Joshua even notes this, in Supernatural, in "Dark Side of the Moon". Unless, the being is older and of greater age than someone/something else. For example, Michael could essentially hide himself from an Angel like Castiel, if they hadn't previously met.