The number 13 used in conjunction with either the number 52 or the number 90 is a shorthand reference to racist propaganda claims by white supremacists against African-Americans to depict them as savage and criminal in nature.
In this numeric shorthand, the number 13 refers to the purported percentage of the U.S. population that is African-American. The number 52 refers to the alleged percentage of all murders committed in the U.S. that are committed by African-Americans. Some white supremacists use the number 50 instead of 52.
Similarly, white supremacists claim the number 90 refers to the percentage of violent interracial crime allegedly committed by African-Americans. Some white supremacists cite the 1994 National Crime Victimization Survey produced by the Justice Department as evidence for the percentage. However, this figure does not show up in the survey itself and is not considered an accurate one. In any case, it should be noted that the vast majority of violent crime is intraracial (committed by a person of one race against a person of the same race), not interracial, in nature.
White supremacists typically employ references to 13 (by itself), 13/50, 13/52 or 13/90 in response to social media posts, and in the comments sections of news stories about crimes in which the suspected perpetrator is African-American. In some instances, white supremacists use the numbers as a purported police radio code, using language like, “We have a 1390 in progress.”