The name is a reference to high-pitched dog whistles that people cannot hear, but dogs can.
Barry Goldwater's Libertarianism was Dog Whistle Code for segregation at the 1964 Republican Convention.
Ronald Reagan's first Presidential campaign appearance was itself Dog Whistle Code, taking place in Philadelphia, Mississippi, the scene of the murder of three civil rights workers.
Originally, Dog Whistle Code for the right to keep slaves, then the right to maintain Jim Crow segregation laws, now the right to oppress any disfavored minorities, women, immigrants, GLBTs and the rest of the riffraff
Deficits don't matter (Ronald Reagan)
Because they hurt Blacks worse than Whites (Lee Atwater, explaining the Southern Strategy and Dog Whistle Code)