In politics there are half a hundred phrases meant as rousing calls to action which only the faithful (of whatever stripe) can hear. It's known pejoratively as dog-whistle politics and designed to alert as many voters as possible while offending few. The phrases usually relate hot-button issues of race, religion, and values (often revolutionary and/or regressive, depending on the country). They are designed to trigger Us v. Them attitudes. See, for example, terms such as one of Reagan's favourites, "welfare queens," or homophobic English-speaking politicians harping on about the "mainstream" (that is, straight white people) or, currently in several countries that fear military juntas and/or populist leaders, talk of "corruption" (which means different things depending who's listening).
Books, though, are not politics. The publisher's blurb about a novel, the flap copy and/or back copy, is designed to entice rather than alarm. Sometimes it must attract its desired audience without scaring off, or even alerting, those who might get it banned. And so was born dog-whistle flap-copy.
Because flap-copy is all about intriguing potential readers, dog-whistle flap-copy seems to be mostly about sex:
- Forbidden love (50s): lesbian sex. Featuring a cover illustration of two women (a well-lit, anguished-looking blonde, and a brunette with very red lips lingering seductively in the shadow). Sometimes the women were referred to as leading twilight lives.
- Forbidden love (60s and 70s): interracial sex. Paired with a picture of a Tara-like antebellum house.
- Forbidden love (lately): interspecies sex (paranormal: vampires and werewolves, etc.) or star-crossed lovers from different clans/cultures (the classic is Romeo and Juliet; lately, a woman from a strict religious culture meeting a man from another—usually but not always—that's more liberal.
- Unexplored pathways of love: anal sex between straight people.
- Dark desires: BDSM.
- Singular erotic taste: general kink.
Of course, all this refers to paper books. I suspect ebooks can be much more straightforward because specialist presses have excellent niche marketing, so finely focused on their audience that few outside that audience know about it. Also, they don't see these books "flaunting" themselves on the shelves and so are not "provoked" by them.
But I'd love to hear others' thoughts on this.
* I suspect non-fiction, especially the crackpot variety, is rife with non-sexual dog-whistlery.