According to Wikipedia and various other sources, the partition type GUID for a BIOS boot partition is 21686148-6449-6E6F-744E-656564454649. This is supposed to represent Hah!IdontneedEFI.
The first line is how it's stored on disk, the second line contains the ASCII values:
48 61 68 21 49 64 6F 6E 74 4E 65 65 64 45 46 49
H a h ! I d o n t N e e d E F I
If we take the previously mentioned GUID, we get:
21 68 61 48 64 49 6E 6F 74 4E 65 65 64 45 46 49
! h a H d I n o t N e e d E F I
Why the difference?