The Baconian cipher:

a   AAAAA   g     AABBA   n    ABBAA   t     BAABA
b   AAAAB   h     AABBB   o    ABBAB   u-v   BAABB
c   AAABA   i-j   ABAAA   p    ABBBA   w     BABAA
d   AAABB   k     ABAAB   q    ABBBB   x     BABAB
e   AABAA   l     ABABA   r    BAAAA   y     BABBA
f   AABAB   m     ABABB   s    BAAAB   z     BABBB

That's the alphabet of the baconian cipher.

To encode a message, a person writes the plain text message and then writes out the message using the five letter code. Over that five letter code, the person writes a false message which is five times as long as the plain text message, and each letter which corresponds to a 'b' is put in italics.

To decode the message, a person puts a 'b' underneath each italic letter and an 'a' under all the rest. Then the message is decoded using the known five letter code.

Hugh Black was the first person to apply Lord Bacon's cipher to the copy of the inscription. With the changing of one capital letter to lower case and counting two 'stacked' letters as one capital, he got a mixed up message that can be phonetically understood as "Francis Bacon wrote Shakespeare's plays." So far, this has been the most viable method of deciphering the inscription. Others have tried, but their methods were inconsistent.