Apple FileVault 2 facilitates full disk encryption and requires OS X Lion or later and OS X Recovery installed on the start up drive. It is easy to detect.
more here........http://forensicsfromthesausagefactory.blogspot.ae/2014/11/imaging-drives-protected-with-apple.html
more here........http://forensicsfromthesausagefactory.blogspot.ae/2014/11/imaging-drives-protected-with-apple.html