Magic numbers for keyring files?

[Robert J. Hansen]

I'm working on adding support for GnuPG keyrings to a file carver (a
forensic tool that recovers data from damaged filesystems, or recovers
things that have been deleted but not overwritten).  Detecting an
ASCII-armored keyblock is pretty easy: look for the "BEGIN PGP PUBLIC"
header.  Binary, though, is still an unsolved question.

Before I start diving into code to find out if the keyring has a
specific binary header I can detect, I figured I'd ask on-list.  :)

Does anyone know of any magic numbers for GnuPG keyring files?