At the very end of an eleventh-century manuscript copy of St Augustine’s Confessions, an Anglo-Saxon scribe wrote “Fknktp Lkbrp χρp prfcpnkB rfddp”. Rather than garbled gobbledegook, these words were written in a simple but popular code: the vowels have been replaced by their neighbouring consonants in the alphabet: a=b; e=f; i=k; o=p; x=u.
The scribe’s words actually read: “Finito libero Christo [the Greek letters χρ is a well-known abbreviation for Christ] preconio reddo”, which is Latin for something along the lines of: “The book is finished, I give a laudation to Christ in return”. Apparently, this scribe was happy that his job was done and rendered thanks to Christ in an encoded message.
The same motivation seems to underlie another encrypted colophon at the end of an eleventh-century Gospel-book made in England: “DFPGRBTKBS AMΗN”:
The first two words of this colophon read “DEO GRATIAS” [thanks be to God]; the last word is “AMEN”, with a Greek capital Eta instead of the E (and a weird M and N, which I haven’t been able to identify).
(colophon — 1: an inscription at the end of a book or manuscript usually with facts about its production; 2: an identifying mark used by a printer or a publisher.)