Dumpster Symbols

From my investigations I have found a genuine demand for a logo or another form of graphic communication to help alert fellow divers about good sources for salvaging. A lot of bins lay hidden down alleys and behind high fences. The concept would be to create a way of directing other divers to them, sharing the knowledge.

The closest thing I have found to anything like this being created is a stencil designed by 'Posterchild' who write a blog entitled 'Blade Diary' http://www.bladediary.com/dumpster-diving/. 

I like the idea itself but it is flawed in many ways in my opinion. I like the fact that there are variations to the logo as seen below; alerting the divers as to the sorts of things that can be found in the dumpster (e.g. the left one alerts the diver there is good, clean packaged food, and the one on the right alerts the diver that there are art type marerials such as paints, wood, cardboard etc.) However, I think in appearence they are too complicated and unclear. The language needs to be more visually clear and universally interpretable. I think it could benefit from being a lot simpler as well. Simple enough that anyone could easily draw/spray/chalk it on.
My other issue with this logo is that it very blatantly alerts the owners of the dumpster. Graffiti is illegal as well giving dumpster divers an even worse name. Also, I worry that divers may not even see the logo until they are already heading over to the bin anyway, which means it hasn't really served much of a purpose. I think it could be far more constructive to formulate a series of visual pointers leading to these less obvious bins, and not making the visual representation so obvious on the bin itself. I like this 'treasure hunt' element to it.