Warning poster by sinks which drain to plants?

I'm involved with a public meeting space, with sinks which drain to plants. I'd like to post an 8.5" x 11" poster at each sink, primarily to ask folks not to put anything toxic down the sink, and secondarily to educate that it's possible to make good use of "waste" water and nutrients.

I'm not creative at all, so I was hoping to find a template I could tweak, maybe something with cute depictions of worms & soil microbes and other friends. I haven't found anything. Does anyone have any pointers before I make something amateurish from scratch?