I truly despise it. I have a dog whistle right here. Go ahead, blow on it. I assure you no one will hear.
That's kind of the point. Only dogs will. The expression is referring to word usage that signals something to a specific group that others won't get.
Since, y'know, aside from the supposedly intended audience, you and every other leftist ideologue on the planet seems to be able to "hear" them, too. You and your brethren would be well served by looking into the psychological concept of "projection" to best explain why y'all are so attuned to these whistles meant only for others. I fact, though, I suspect the only whistling to be heard is the sound of the air rushing into one of your ears and out the other through the empty space that lies between.
-Samantha Jones, SatC