Copies of materials that genealogists use in local courthouses are considered record copies of the original document. All of those deeds in the deed book from the 1830s are not originals, they are handwritten transcriptions of the original. The original normally was given to the person who obtained the property via the deed. The clerk's job was to transcribe the document as accurately as possible, making no changes--even when errors were obvious.
So that's why in some of those old books the signatures match the rest of the handwriting. It's not really the signature, it's the clerk's handwriting from start to finish.