Wall mirrors (if not wanted) should not be covered. They should be removed from the wall.  This can be done by a professional glass shop using suction cups to "pop" the mirror from the wall.  Unfortunately, depending on the condition of the glue and amount used, there will more than likely be some damage to the wall that will have to be repaired also.  The reason for not covering or painting them would be that if someone, not knowing they're there, may try to nail through them to hang a picture or something and break the mirror and possibly be injured.  (answered by A-1 Glass & Mirror of WNY Inc.)