What I'm describing is volunteer labor. As long as there's no obligations, I'm free to do it or not, at my leisure.

If you want to put up a sign, go for it. Maybe I live near you (doubt it), or maybe there's another busybody that likes to organize stuff. You might get robbed, or you might get some free labor, you never know! But an invitation is a prerequisite. I have helped people clean up stuff because they asked nicely, and I would do so again if more people asked. It turns out, I like helping people, and I don't really care if they're making a profit or not (I've cleaned up for-profit businesses as well, because I like the service they offer).

It's the same general idea as those "free small libraries" people put out. They put in some amount of effort to keep it orderly, and invite community members to do the same. Sometimes it works out and people exchange books and keep the "library" orderly, and other times people take advantage and steal the books to resell online or something. Which one happens depends on your local community.

If you pay someone, you'll probably get the results you want. If you don't, well, it depends on who chooses to do the work, if any.