A padlock icon on hard drives in the Windows 10 File Explorer indicates that the hard drive has been encrypted with BitLocker or Device Encryption program.
BitLocker, present in Pro and Enterprise editions of Windows 10, allows users to encrypt drives to secure the data. The built-in encryption program adds a padlock icon on hard drives in the File Explorer so that users can easily identify the hard drives that are protected by BitLocker.
The lock means the drives are encrypted, and if unlocked means the hard drives are currently unlocked so that you can access the data. Depending on the state of the encrypted hard drive, you might see one of the following three icons on drives.
Locked padlock: BitLocker enabled and locked state: Volume is inaccessible. You will need to type the BitLocker password to open the drive and access the data in it.
Unlocked padlock: BitLocker enabled but unlocked state: Hard Drive is encrypted and keys are protected. You don’t have to enter the BitLocker password to open it.
Unlocked padlock with yellow warning triangle: BitLocker is inactive or the protection is temporarily suspended: Hard Drive is encrypted but everyone has access. This icon is also used to indicate the BitLocker is pre-provisioned. You can resume the BitLocker on the drive or disable the BitLocker for the drive to remove the icon.
Resume BitLocker protection for hard drive
Right-click on the hard drive and click Resume BitLocker protection option. Alternatively, you can restart computer once to automatically resume the BitLocker protection.
Disable BitLocker protection for hard drive
Step 1: Right-click on the hard drive for which you want to turn off the BitLocker protection and click Manage BitLocker option to open the BitLocker Drive Encryption window.
Step 2: Click on Turn off BitLocker link.
Step 3: Click Turn off the BitLocker button to turn off the BitLocker encryption for the drive when confirmation dialog shown.
Step 4: Windows 10 might take minutes to hours to decrypt the drive, depend on the size of the data and drive.
Reference: BitLocker overview at Microsoft Docs