Q:

Can the Diffie-Hellman protocol be used as a base for digital signatures?

I am implementing a custo crypto library using the Diffie-Hellman protocol (yes, i know about rsa/ssl/and the likes - i am using it specific purposes) and so far it turned out better than i original expected - using GMP, it's very fast.
My question is, besides the obvious key exchange part, if this protocol can be used for digital signatures as well.
I have looked at quite a few resources online, but so far my search has been fruitless.
Is this at all possible?
Any (serious) ideas are welcome.
Update: 
Thanks for the comments. And for the more curious people:

my DH implementation is meant - among other things - to distribute encrypted "resources" to client-side applications. both are, for the most part, my own code. 
every client has a DH key pair, and i use it along with my server's public key to generate the shared keys. in turn, i use them for HMACs and symmetric encryption.
DH keys are built anywhere from 128 up to 512 bits, using safe primes as modulus.

I realize how "pure" D-H alone can't be used for signatures, i was hoping for something close to it (or as simple).

A:

It would appear this is feasible: http://www.quadibloc.com/crypto/pk050302.htm.
I would question why you are doing this though. The first rule of implementing crypto is don't implement crypto. There are plenty of libraries that already exist, you would probably be better off leveraging these, crypto code is notoriously hard to get right even if you understand the science behind it.

