One of my pet peeves at the cemetery is that people leave trash behind their headstones. When they come to put in new flowers or other orniments, they simply take the old stuff and place it behind the stone. This occurs in sections that have trash barrels.
I equate leaving trash behind your stone with going to someone's house, bringing a cup of coffee, and leaving the empty cup behind the sofa. You would never do that (I hope), but some people feel it's not their job to remove what they originally brought in.
There are thousands of headstones in the cemetery. There is absolutely no way anyone is going to visit the backs of every stone to pick up trash. That's why there are barrels.
Another pet peeve is when people throw plastic trash into the woods. There are large tracts of woodsy hills in the cemetery, and I have no problems with people throwing leave, grass, pumpkins, even bush clippings well into the woods. It all turns to loam eventually. But plastic, glass and metal will remain for many many years, and they will look ugly for years. Put these items in, or at least by, the barrels for pick up. Any plants or planters should have all non-organic matter removed (ie bows, plastic berries, etc) before they are tossed.
Last pet peeve is when people bring in new decorations, but do not remove the old ones. "Out with the old, in with the new" please. It's cleaner, neater, and prettier, and easier to maintain.