On many forums. Cough reddit. You can barely say anything slightly spicy without a warning/ban so people are constantly talking in riddles to say more sinister stuff especially if there is implication of encouraging direct action. This is like that. At 30khz it says "get your jammers out!"

To a dog the whistle is explicit. (Not using dog as a derogatory or complimentary term here... more the fact the dog can hear the high frequency)