i have a few, my spell BoS has been seen by people mostly in my coven, but i think i'm the only one who's touched it. i think my friend might have flipped through once though. no one's touched it because no one needs to, and i don't really mind if they do. we just know most items we use are charged by our energy, so unless we ask first, we assume every object is off limits from being touched until otherwise specified. that's basically why the no touching thing is around, because you;re charging it with your energy.
the no seeing is more historical. with the witch burnings you couldn't leave your families BoS on a table open all the time anymore, you had to hide it under a floorboard and only let those in your coven see it for your safety as well as the covens.