In politics, a dog whistle is the use of coded or suggestive language in political messaging to garner support from a particular group without provoking opposition. The concept is named for ultrasonic dog whistles, which are audible to dogs but not humans.
-Wikipedia
The dictionary site www.ludwig.guru defines by example: When political parties have policies that will appeal to racists while not being overtly racist, they are indulging in dog-whistle politics.