Determine if file or directory is encrypted?

If you're using FileVault 2 (OS X Lion and newer), the entire boot partition will be encrypted, which includes your home folder as well as Applications.

I ran the following command and part of the output shows I am using an encrypted, unlocked volume:

ashley@sidekick-4:~$ sudo diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           *249.8 GB   disk1
                                 Logical Volume on disk0s2
                                 2DDC5CBD-1B65-403E-9D4F-9424BC764433
                                 Unlocked Encrypted
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS Time Machine Backups    2.0 TB     disk3s2
ashley@sidekick-4:~$

Since Lion OS X uses full disk encryption for filevault2. Therefore it creates corestorage volumes on your disk and overwrites the entire contents with encrypted data. This encryption process takes a while, depending on your system speed. Only after that your disk is "secure".

You can see the partition's encryption status either in the System Preferences > Security & Privacy > Filevault. Or use the diskutil corestorage list command in Terminal. Look for the fields Conversion Status and Fully Secure. I had cases when the encryption was not successful but received no error message.

    > diskutil corestorage list
    CoreStorage logical volume groups (1 found)
    |
    +-- Logical Volume Group XXX
        =========================================================
        Name:         10.8
        Status:       Online
        Size:         669162500096 B (669.2 GB)
        Free Space:   16777216 B (16.8 MB)
        |
        +- Logical Volume Family XXX
            ----------------------------------------------------------
            Encryption Status:       Unlocked
            Encryption Type:         AES-XTS
            Conversion Status:       Complete
            Conversion Direction:    -none-
            Has Encrypted Extents:   Yes
            Fully Secure:            Yes
            Passphrase Required:     Yes
            |
            +-> Logical Volume XXX
                ---------------------------------------------------
                Disk:               disk1
                Status:             Online
                Size (Total):       668826951680 B (668.8 GB)
                Size (Converted):   -none-
                Revertible:         Yes (unlock and decryption required)
                LV Name:            XXX
                Volume Name:        XXX
                Content Hint:       Apple_HFS