Here are a few additions I would make to the building code for public restrooms:

1. All restroom doors must open outward. If the restroom is large enough to contain stalls, it must be possible to open the outer door simply by pushing with the toe of one’s foot. Sharply-turning doorless corridors that block sightlines are acceptable.
2. If it is necessary for a restroom door to lock (as is the case with single-person restrooms), handles are to be used rather than doorknobs. Additionally, attempting to open the door from the inside must automatically disengage the lock.
3. If a restroom displays a sign asking people to wash their hands before leaving, it must be directed at all users of the restroom, not only at employees.
4. If the outer door can be opened without the use of one’s hands, choice of paper towels, air dryers, etc. is left to the discretion of management. In the event that opening the door does require hands, drying methods provided must include paper towels.
5. At least one trash receptacle must be within casual tossing distance of the outer door.

Of course, these are mostly ways to mitigate the fact that a disturbing number of people won’t take an extra 30 seconds to clean up on the way out. A better solution might be a device I saw in The Far Side: an alarm which went off whenever someone left the restroom in a less-than-sanitary state, with a blazing sign proclaiming "Didn’t wash hands!"