Next time, rather than take the keys and post it here, make a makeshift sign saying here are your keys with the keys on the sign, or if that isn't possible put them on a stick on the trail, etc., just make them easy to find when they come back to look for them. The person that lost them surely went back to look for them when they couldn't unlock their vehicle and drive home.
Yup that sounds like the perfect idea. Myself or some crackhead can come along, find the keys and take off with that persons car.