The thing is, anyone can go into court and say "That's not my signature, I never signed that or saw it before." Heck, one summer I signed for tens of thousands of dollars of UPS deliveries as "Washington Irving" (as in Catch-22) and the drivers never even read it, much less questioned it.
But on the other hand, if there's a notarized document, and you say "I never saw that, I never signed it" and the notary has done their job and perhaps made a photocopy of your government photo
ID? Folks are liable to question whether you DID sign that document, or if there's some great conspiracy against you.
There was a big murder trial in Scarsdale NY back in, maybe the late 80's. Both sides presented "original" copies of a Sprint phone
bill, one showing the defendant was someplace else making a phone
call at the time, the other "original" not showing any such call. This at a time when commercially laser-printed bills were not so easily faked. I forget who eventually "proved" anything over this, I think the court eventually just threw out the questionable bill, in a sea of other evidence and charges.
The whole purpose of notaries, is to provide a third-party objective attestation as to who
actually signed a document. (Along with when and where.)