No bottoms on the sink

Ruby and I were at the library and she was using the potty. She looked up on the wall and noticed a "no smoking" sign. She looked at me and said, "Mommy, that sign means don't pee in the sink." I thought that was a really strange thing to say, so I asked her why and she said, "because that is a bottom sitting on the sink and we don't sit on the sink." I looked up at the sign and had to laugh. The smoke on the cigarette really does look like a bottom.