A dog whistle is a whistle that dogs can hear but humans can’t. “Dog whistle” also refers to a word or phrase that is like a secret code for something else.
Here is how the first kind of dog whistle works: A human blows into the whistle and any dogs that have been trained to respond to it come running. Nearby humans don’t hear anything.
The second kind of dog whistle works basically the same way. A human says a special word or phrase into a microphone, and the people who have been trained to respond to it come running. The word or phrase is common, so the rest of the people listening don’t hear it in the same way.
The idea is: People are as easily manipulated by words as dogs are by the whims of the people they are inclined to be loyal to. Here at Wordmonster, we think that’s probably true. But there is an obvious problem with this expression: No one ever thinks of him- or herself as one of the silly, bounding, slobbering dogs. Verbal dog whistles are for other people — people who don’t think.
It’s never a good idea to flatter yourself.