Is there a reliable way of determining if a Windows 7 volume is encrypted using bitlocker other than using 'manage-bde.exe'? Are there registry values or other files that can be read that will give this information?
See this blog post from MSDN blogs.
Quoting from blog:
A BitLocker volume has a clear-text BPB much like FAT and NTFS. The BPB is located at the first 0x54 bytes of the first sector of the volume.
BitLocker stores multiple copies of the volume metadata, and the first copy can be located from information in the BPB. The byte offset of the first metadata location is calculated as MetadataLcn * SectorsPerCluster * BytesPerSector.
There is also WMI query
GetEncryptionMethod available, as instructed in blog post.