Replying to Leaving presents in the toilet

Hey NS. I'm an RA and am having issues with residents not flushing the toilets after using them. It's pretty gross and makes the bathroom smell. I've e-mailed them once about it and apparently still have some people who didn't learn when they were 3 to flush the poopy down the hole. I want to make a funny sign of some sort that is clean and humorous to remind people to flush. The problem is I am not artistic and only have MS paint at my disposal. A few things I was thinking of was an Uncle Sam or Smokey the Bear public service announcement. Can anyone with some art/photoshop skills throw me a bone and help make something that will get the point across?