It would be possible to rectify this by putting a dry-erase board or blackboard on the outside door of each stall, with a piece of chalk or a pen on a string. People would mark a tally each time they used a stall, until a janitor comes along and cleans the toilet and the board. This way patrons could see which stalls had been used more heavily, and adjust their habbits to provide a more consistently clean restroom.

Of course, some jokers might come along and erase the board or add in dozens of tallies, or simply add no mark at all. An electronic counter might be best if this problem came up.