Mail Art: An Annotated Bibliography by John Held Jr.
Interesting for specialists only, this is essentially expanded bibliography of Mail Art with 2199 positions. It has 2 entries for Serge Segay and one for Rea Nikonova. This is what it says about Serge Segay's article "Where the Secret is Hidden" in magazine Iskusstvo, published in 1989:
This book was published in 1991.