Take a Sharpie pen or even a piece of clear tape and either make a mark, or place the tape around the seat post where the seat post meets the tube. That way any shop that has to remove the post to put it on a rack will know where to set it when they are done. And you will always know at a glance if it has slipped, or is otherwise in the wrong place. And if you later decide it's too high/low, you have a reference point for making adjustments.