What level of play? When/how was it caught?
If this is an informal house league game played under NFHS with parent scorers and parent coaches, one coach comparing the book to his own in the bench area, it is one thing. And if you see him pick it up or holding it by the bench, I would just say put it back. Even if you see him at the tail end, if it doesn't look like he was altering the book, do you really want to issue a T here?
If this is a real HS game with real scorers and coach walks with book, follow the rule. You have to recognize where you are and the formality of the situation before making this call. On court stuff, you always follow the rules. Administrative stuff in informal games, you look at the situation and decide.
A good example of this is that nobody gives starters in any games I have coached except at Nationals. Obviously no Ts are issued for this
But if it was the finals of the National qualifier and the book disappeared at halftime, I would probably take more issue with this than at a meaningless fall league game.