I think the point of this sign is that you're not allowed to defecate outside, but I also read it to mean that there's no charge for defecation.   

Any Tour rider will tell you that staying in a town, as opposed to camping out in the bush, was a mixed blessing.  On the one hand, you've got restaurants and running water and laundry facilities and pharmacies and Coca-Cola.  On the other hand:  Sudanese public toilet. 

The phrase Sudanese public toilet should strike terror into the heart of the most courageous of men and women.  It should strike terror into their hearts in the same way that "nuclear launch failure" and "President Schwarzenegger" should. 

I'm not kidding when I say that many of us preferred to camp in the middle of nowhere, digging a hole in the dirt, than to stay in a place where your shower and your toilet were the same thing.  You don't want to kiss anybody who disagrees.