I dont want to give a law lesson here, but from my profesional experience, I can tell you that you better wake up early if you intend to prove that you did not consent in whole to what appears in a document that you have signed )  Further than that, signature also gives a somewhat fair idea of the concept (notably pointing out that a signature is evidence of the provenance (identity) of the document... signing a document is proof that it comes from you personnaly, what does not mean that it cannot also come from other persons as well).  For instance, you can have 3, 10, 20 parties to a contract, all can be held personnaly to the whole unless stated otherwise.