Retrieving signature from message that was encrypted and signed in one step

[Patrick Chkoreff]

I have a message that was encrypted and signed in one step.  When I 
decrypt it, I can read the message and see that the signature is valid. 
  So far so good.

I would now like to relay this message to a third party so he can 
verify the signature too.  But as far as I know, GPG has no way to do 
this.

Can GPG do this?  If not, why not?  Is this lack of ability actually a 
feature?  I suppose it could be a feature, because this gives the 
sender a way to prove to ME that he signed something, without giving me 
a way to prove that to anyone else.

Is that the reason why what I want to do is not possible with GPG?


Thanks,
Patrick