Aliens on the bus and other things

Yesterday noticed there is a strange series of signs on the bus- this is under the "what you cannot do on the bus"- there are these little pictures to try to illustrate for you, or maybe for people who don't know English. 3 of the symbols make some sense: no eating, no music, no skateboards and then the last, is literally of a hot air balloon. Can't figure that one out. I will try to get a picture of it though.