No Symbol - International Standards

International Standards

While the "prohibition sign" has been so widely used in advertising and promotions that now any variation of the design flipped left or right or varied in hue is considered acceptable and recognized by the general public as a symbol of prohibition, it is still governed by local and international standards. The standard definition of the no symbol comes from the International Organization for Standardization.

In 2002, ISO 3864-1 was published (a revision of a standard first published in 1984). The introduction includes language on the need for using as few words as possible to convey information.

ISO 3864-1 sets the rules for the color and shape of safety signage, as well regulating the incorporation of text according to viewing distance and sign size. The range of color and shape defined in this standard for the "prohibition symbol" or "no symbol" is defined as "a prohibition surround shape (red circular band with a red slash going from the upper left to the lower right) over the top of a black graphical symbol."

Since the standard is not published freely (ANSI sells it for US$104, while ISO sells it for CHF 102,00) and many examples seen in public diverge from the standard, many symbols and public signs using it have not actually been based on the official standard, but instead on inexact copies or interpretations of signs or symbols seen by each graphic artist. This has led to wide variations in color and dimensions. The most common variations seen are brighter reds than specified in the standard and either a much thinner width for the line and slash, or about the right dimensions but using the same width for the slash as the circle (the standard specifies a width that is 80% as wide as the circle). For example, compare Image:No smoking symbol.png (a non-compliant representation) with Image:ProhibitionSign.svg (a representation drawn using the ISO standard).