I have googeledd that and figured out it is a sign that bitlocker Now, just a few days ago I realized that on fresh Dell notebook installs, factory image of Dell, the C-drive (it's usually our only drive) is shown with a yellow exclamation mark in file explorer. But this is optional, none is forced to do so. To save the recovery key txt file on a certain share, BitLocker key is also saved to computer object in AD. In our company we have a global GPO which, if one wants to encrypt his harddrive with BitLocker, to be prompted Since a while we are experiencing some strange behavior with Windows 10 (I think it only apply to Creators update), Dell Notebooks and Bitlocker.
