The signature is part of the body, so no, there isn't really a way to just remove the signature, unless you knew that every signature was going to have the exact same format.
If you knew that every signature was going to come after 10 hyphens, like this
Lorem ipsum lorem ispum.Lorem ipsum lorem ispum.Lorem ipsum lorem ispum.
Lorem ipsum lorem ispum.Lorem ipsum lorem ispum.
----------
Your Name
If that is the case, then you could just do
$message = explode('----------', $body);
Where $message[0] would be the body, and $message[1] would be the signature.