Clearly you have not ridden the buses in LA then. I did this for 2 years to get about the westside. Even imagining that people would read the sign, or know the English language clearly enough to do so, is laughable. The average bus rider in my small experience (not talking about the actual average, that I do not know) is typically Spanish speaking, is crazy drugged out/drunk, or will not care no matter how much you try to reason with them. I kid you not, I have seen on more than one occasion a homeless person heave feces at the buses that pass them by when they are too full to legally allow more people on. Maybe not most, but enough of the population of passengers are too nuts to reason with that trying to enforce a disembark only policy will lead to deaths of drivers (not that the drivers are all that different than passengers either, you cannot believe that some are considered qualified to drive by any rational person). At the end of the day, trying to deal with real people leads to unreal problems.