A brief note left on the pack could be helpful. Just "Pack was noted here (date/time), hope there's no problem." would at least cause great concern on the part of the next hiker to see it the next day.
I stole a guys GPS once. It was sitting on a post, because it was soaking wet when it hadn't rained since last night I assumed it had been found and placed visible some time ago, lesser-used trail so I took it. I was able to find the guy's phone number on the GPS and called him. Turns out he had dropped it in the water and laid it there to dry while checking out the shore.[:I] Hey, guy whose name I can't recall: Really sorry about that, it was truly done with the best intentions. And you do have your GPS back.