A mezzanine stretches above the BMT Broadway Line platforms, ramping down to a control area at its south end, where there are stairs down to the Broadway Line platforms and transfers to the other platforms. Along the mezzanine and adjacent passageways, the tops of the walls contain friezes made of raised geometric patterns on the rectangular tiles. White-on-green tiles with the number "14" are placed at the tops of the walls at regular intervals, while white-on-green "Union Square" tablets are installed below the friezes. Rectangular red metal frames also surround sections of the original wall. The mezzanine is relatively shallow, and because it was built with insufficient clearance, Union Square Park was raised by to accommodate the station. Imprinted on the walls are over 3,000 stickers with the names of victims of the September 11 attacks, which were put up by artist John Lin and sixteen friends on September 10, 2002. The stickers were not sanctioned by the subway system's operator, the Metropolitan Transportation Authority, and have deteriorated since they were placed.