"Wash Me" isn't just seen on dirty vehicles in the USA. Here, we have another example of someone hinting for that result. I think the picture drawn on the side is actually of a house. It may look odd to you, but in African terms, that round hut is really quite accurate.
Yes, driving in Uganda you can find all sorts of interesting signs and expressions. This one may seem funny at first (who wouldn't want to avoid child sacrifice?) until you know that witchcraft and the like are COMMON here in Africa, with abductions ending not in ransom but in human sacrifice to supposedly obtain wealth or some other thing. Not a week goes by, or so it seems, that someone isn't taken and killed for these purposes. Pray that Jesus will penetrate the hearts and minds of the people here in whatever ways He can and will move!