'Eduardus is my proper name' (near bottom of page)
It is only reasonable to suppose that Edward de Vere, 17th Earl of Oxford, writing under the pen-name William Shakespeare, would have left a clue to his authorship in the plays themselves.
It is unlikely that this clue would have consisted of a cipher. Ciphers require a key, or the precise placement of text, neither of which was a practicable option.
A better solution was for Oxford to allude, within the plays, to some written work outside them. This allusion would, of necessity, have to be to a work which was both widely available and very well known to Oxfords contemporaries, and which Oxford could be certain would be equally widely available and well known to succeeding generations.
The choice was Lylys Latin Grammar, a work committed to memory by every educated Elizabethan, and used as a standard grammar text until the eighteenth century.
The facsimile reproduced to the right shows the page in Lylys Latin Grammar to which Oxford referred in the Shakespeare plays, a page which contains the sentence 'Edwardus is my proper name'.