On September 14, 2010, she wrote a very informative and critical article in the Design Observatory Group website entitled "The Black Rule". According to Wild, the Black Rule is "intimately connected to a typographic grid, and the paper it's printed on." The color black symbolizes importance and, in the case of The Black Rule, formality. The Black Rule also defines the dimensions of a piece of paper and separates the hierarchy of heads and subheads. The text that is used for The Black Rule is, commonly, Helvetica. This is evident in our every day life whether we notice it or not is the question. The most noticeable signs of The Black Rule is on subway signs or on U.S. Park Service maps. Wild was not the founder or inventor of The Black Rule. Massimo Vignelli is credited for discovering The Black Rule. This became his own brand although it was not typical, at the time, for designers to have a certain icon to represent his or her own work. Vignelli's most popular works is designing the American Airlines logo and the iconic New York City Subway maps.