Washington State University
Infirmity doesn't explain the first three even more primitive signatures. This does not strike me as the handwriting of a very literate person. The rest of Shakspere's family seems to have been illiterate, signing their names with an X. And note that none of these signatures is spelled "Shakespeare" nor indicates a long 'a' in pronunciation.
"Shake-speare," the designation of the author of the works, is a pseudonym, and this would have been rather obvious to the Elizabethans.
In 1578, Gabriel Harvey wrote a glowing tribute to Edward de Vere, 17th Earl of Oxford. Here is one passage:
O thou great-hearted one, strong in thy mind and thy fiery will, thou wilt conquer thyself, thou wilt conquer others; thy glory will spread out in all directions beyond the Arctic Ocean; and England will put thee to the test and prove thee to be a native-born Achilles. Do thou go forward boldly and without hesitation. Mars will obey thee, Hermes will be thy messenger, Pallas striking her shield with her spear-shaft will attend thee.Dorothy and Charlton Ogburn in This Star of England append this note from Edwin Reed's Prefatory Address to the Folio:
In Grecian mythology, Pallas Athena was the goddess of wisdom, philosophy, poetry, and the fine arts. Her original name simply Pallas ... from pallein, signifying to brandish or shake. Athens, the home of the drama, was under the protection of this spear-shaker."It may be added that the helmet she wore was supposed to convey invisibility. To the young Elizabethan who had been acclaimed the champion spear-shaker of the lists, whose crest, as Lord Bolebec, was a Lion shaking a broken Spear, and who was himself a dramatist and patron of writers, these facts of which Harvey was reminding him would have had considerable relevance and interest" (Ogburn & Ogburn 146).
David, Frank, MD. "Relevance of Shakspere's signatures: a comparison of autographs of Shakspere and his contemporary actors and writers." The Shakespeare Oxford Newsletter 45.1 (June 2009): 8-13.