Book In-Jokes in...
Object-Oriented Software Construction
(2nd Edition, Prentice-Hall, 1997)
While the book uses the Eiffel language as its notation, the language itself is not mentioned by name except as the very last word in the text. Most readers will notice that the Epilogue is titled “Epilogue: In Full Frankness Exposing the Language” -- the first letters forming the word “EIFFEL”. But few readers will notice that the language is also hinted at earlier. The first chapter (not the title, but the chapter itself) starts with the letter “E”. The second starts with “I”, and so on, so that the first six chapters form “EIFFEL”. This is then repeated, so all in all, the 36 chapters present the word “EIFFEL” six times.
(Also in the Bookshelf: a full review of this book.)