For thousands of years certain numbers have had a symbolic meaning beyond their mathematical meaning. In some cultures the number '4' is holy as it corresponds to the four corners of the world; in other, especially biblically oriented, cultures '3' is a holy number (e.g. "the father, the son, and the holy ghost"), but already Pythagoras believed in the magic of numbers including, incidentally, the cardinal number "3".
From the Bible we know the number "666" as a symbol of the Devil, and other numbers are thought of as "unlucky", thus in many American towns there's no 13th Street (the street is there, but usually it's called something else, e.g. "Division") just as most buildings don't have a 13th Floor, but call it "Management" or "Service" or anything else that is neutral. Same thing for many airplanes.
In modern American English certain numbers carry more than just a symbolic meaning. The "411" that dials the telephone information service has come to mean "information" itself. Other numbers refer to specific organizations.
Here's a few to avoid:
- '14' represents the number of words in the slogan for the white supremacist movement, ”We must secure the existence of our people and a future for white children.”
- '88' is a neo-Nazi greeting. H is the eighth letter of the alphabet, and eight twice means HH or ”Heil Hitler.”
- '5' represents the number of words in the slogan, ”I have nothing to say.”
This phrase is used by white supremacists as a code of silence and to avoid prosecution.
- '311' is a symbol of the Ku Klux Klan. K is the 11th letter in the alphabet, so three times K is KKK. It may also be written as ”33/6,” with the six representing the current era of the Klan.
- '666' is used by white supremacists to symbolize Satan or evil.
- '83' is used by racist groups that consider themselves Christian. It stands for ”Heil Christ” (H is the eighth letter of the alphabet and C is the third).
- '100%' is used by white supremacists to signify pure Aryan or white roots.
It also represents the ”need” for a pure white race.
- '4/19' is sometimes used as a tattoo by antigovernment racists. The number represents the date of two events: The siege at the Branch Davidian compound in Waco, Texas in 1993 and the 1995 Oklahoma City bombing by Timothy McVeigh.
- '4/20' is a tattoo used to affirm neo-Nazi beliefs. It is the day Hitler was born.
Sources: "Hate Springs Eternal," Harper’s, 1 March 2000; "Hate on Display: A Visual Database," Anti-Defamation League (http://www.adl.org)