Knowing what you are looking at is key to any level of genealogical analysis. Making the most out of any record and not becoming confused depends on understanding the material in front of you.
That’s why this is not the signature of John and Milly Sledd.
It’s the clerk’s transcription of their signature because this deed book contains word-for-word transcriptions of deeds that were brought to the county office for recording. The purchaser of the property kept the original deed. That is the record that had the actual signatures on it. That was the original signed document.
John and Milly’s signatures may have looked nothing at all like what is pictured in the deed record book. John and Milly signed the original deed, but their hands did not touch this page in the record book and neither did the writing instrument they used to sign the original.