Well, I wouldn't "lock it away" so much as "toss it aside". When it comes into my hands, I would just think it's a normal notebook that some Death Note fan decorated. I wouldn't give it to a lost and found if it were blank inside, because I kinda like notebooks with quirky decorations like that. So I'd either toss it aside and forget it existed or I'd keep it and just use it as a normal notebook or a sketchbook or something. If I wrote a person's name in it (to record their contact info or something) and then they died, I really would think it was just a coincidence.