Standard vaulted stations are lined by small white earthenware tiles, chosen because of the poor efficiency of early twentieth century electric lighting. From the outset walls have been used for advertising; posters in early stations are framed by coloured tiles with the name of the original operator (CMP or "Nord Sud"). Stations of the former "Nord Sud" (most of line 12 and parts of line 13) generally have more meticulous decoration. Station names are usually inscribed on metallic plaques in white letters on a blue background or in white tiles on a background of blue tiles.