When hosting dinners for foreign dignitaries the Swedish Court put discreet placemats in the same fabric and colour as the tablecloth at the seats of the hosts and the guests of honour if they are commoners. Why you may ask? The reason is that according to old court traditions a royal should never share a tablecloth with a commoner so this is a way to get around this.
How is it determined with foreign dignitaries which are commoners and which are not? It may be a fairly simple matter with dignitaries from other European countries, but I imagine the class distinctions in some African or Asian societies will not correspond to the European concepts of commoner and nobility.