The number 737 is a numeric symbol used by Public Enemy Number 1 (PENI), a California-based white supremacist gang present on California's streets and in its prisons. The numbers 737 correspond to the letters P, D, and S on a telephone keypad; the initials PDS stand for Peni Death Squad, another name for the group.
The number combination 14/23 is a numeric symbol associated with the Southern Brotherhood, the largest white supremacist prison gang in Alabama. The 14 is a reference to the white supremacist "14 Words" slogan ("We must secure the existence of our people and a future for white children"), while the 23 refers to the "23 precepts," a list of rules that Southern Brotherhood members must follow.
The number combination 23/16 is a numeric symbol used by white supremacists, particularly common on the West Coast. Substituting letters for numbers, the 23/16 equates to W/P or "White Power." Sometimes the combination is rendered as 16/23, in which case it is often intended to mean P/W for "peckerwood."
The number 33 is used by Ku Klux Klan adherents to signify the Ku Klux Klan: since the 11th letter of the alphabet is K, three Ks signify "KKK" or the Ku Klux Klan. Klan members will frequently follow this with the number 6, to indicate the historical "era" of the Klan they think the Klan currently is in.