To prevent littering and waste, it's important to remind everyone to clean up after himself or herself. And if you want to make sure the message really sinks in, a little creativity and humor can really help.
Write the words, "Sorry, but the maid quit. Please clean up after yourself." Or draw a picture of a sign that reads, "Gone Fishing" next to a mop and bucket. Or you could write a sign that reads, "Until you can afford a maid, you have to clean up after yourself." You can use cartoon drawings of maids as well. They could be holding picket signs saying they're on strike.
Draw a sign with a stern-looking adult figure pointing out, "I'm NOT your mother. Clean up after yourself." Or you could draw a picture of a janitor with a caption that reads, "Do I look like your mother?" Or point out that the visitor's mother didn't raise him or her in a garbage dump.
Make a sign pointing out that we have only one planet. You could draw a picture of Earth. Or draw a picture of the planet covered in trash and ask, "Is this what you want to call home?"
Draw a picture of a dog using a poop scooper, or a bird using a spray bottle and rag to clean a windshield. Then write out "Please clean up after yourself." Or draw a man dropping trash as he walks, and have a baby cleaning up after him, tossing the garbage in a trash can. You could simply put up a sign that reads, "Don't feed the roaches. Clean up after yourself." Or draw a picture of a fairy buried under a pile of cigarette butts. Write, "The cigarette fairy called in sick. Clean up after yourself." You could also make a sign pointing out that unless everyone cleans up after himself or herself, only the robots will be left. Draw a picture of a robot standing on a garbage pile. The sign could read, "Clean up after yourself or the robots win."