Etiquettes/car not for sale

Rotterdam -  It is prohibited to deal in used cars in this street, 
Article so-and-so of Rotterdam’s local regulations. This sign made me think of a lecture I once took in art school, about etiquette in the Middle Ages. One of the examples cited was the rule that you should not blow your nose with the tablecloth. But then again, if you need a rule like that, is clear that apparently people do blow their noses with the tablecloth.
Maurice Bogaert – Rotterdam Lab