simple you can do many things to achieve this. A spell to make something unnoticeable will help but it will not keep someone from actually looking at it and reading it. If you wish for people not to read it then you should keep it close to you.
Now, I'm not david copperfeild, so in all honesty I dont know how to make things invisible. But (someone please correct me if I'm wrong) wiccans use the pentacle as a symbol of protection.
I like the symbol because it represents the 5 elements of nature. I may not wiccan in the strictest sense (since I haven't been inducted or ordained into covens and groups), but I do feel very strongly towards this symbol. And yes, I do have it on the front page of every book.
If you don't want anyone to see the pentacle, you can draw it with your finger and in your mind's eye, see it illuminate in blue light. Speaking of which, blue is a colour that's attributed to Archangel Michael, the angel of protection. So you may wanna light a blue candle while you're drawing the pentacle.
After all, thank the pentacle and Archangel Michael for assisting you.
But, do let me warn you about one li'l thing. If you leave this book next to your home landline or the magazine rack in your living room, chances are someone will pick it up and read it
:-). So apart from the spell, you may want to try a box or a draw with a lock and key.
TIP: If you want it hidden, then don't go turbo on decorating it. It will just attract unnecessary attention.