Other forms: dog whistles
A dog whistle is a whistle that makes sounds so high-pitched that humans can't hear them, but dogs can. But it also has a second meaning relating to the idea of sending hidden messages that only some people will understand.
Dogs can hear higher-pitched noises than humans, so dog whistles are used to draw dogs' attention without humans hearing. They are often used when training dogs and when giving them commands. In politics, a dog whistle is a word, phrase, or some other symbol that is used to mean something different than what it appears to mean on the surface. Only people with certain, often controversial, political beliefs are meant to understand. For example, wearing a certain color, pin, or pattern, or using a particular phrase in a speech, could send a message to people in the know.