The phrase ‘even a police man will know this’ is used often to ridicule someone’s ignorance on some trivial matters or if they are slow to grasp something. For some historic reasons that I am not aware of, policemen are considered somewhat slow in their head.
But I think it’s time to give this a second thought.. Here is a very creative poster on road safety from Bangalore.
If you don’t quite get it, you may want to read the story on How did Lord Ganesha get elephant’s head? here.