I'm not sure how many rest areas there are in Michigan but on some stretches of road, there is at least one every 30 to 40 miles. There are quite a few that they try to make look nice. They will have flower gardens that exhibit the native flora.
But of course, you have rude people everywhere. I'm not sure why people would walk through a flower bed but they do. Not that signs really help other than illuminating the rudeness of others. But this is one of the reasons why we don't have nice things in many places.