On their Shakespeare’s Signature page the The Shakespeare Birthplace Trust (SBT) says
There is ongoing discussion amongst scholars as to whether all of these six signatures were actually written by Shakespeare himself or by legal clerks involved in the preparation of the documents.
Is it possible that the articles written by Robert Detobel or Matt Hutchinson may have played a role in crafting the SBT paragraph?
You can read more about the signatures in this summary of Hutchinson’s work by Dorothea Dickerman.