Google AI:
In politics and social commentary, a dog whistle is an expression that has a secondary meaning intended to be understood only by a particular "in-group"
The Literal Origin: Actual dog whistles emit high-frequency sounds that dogs can hear, but humans cannot.
The Figurative Meaning: A speaker uses words that sound neutral or "innocuous" to the general public—like "traditional values" or "inner city"—but signal controversial or biased messages to a specific group. This allows the speaker to maintain plausible deniability if they are accused of being offensive.
"This talk had more dog whistles than a canine construction site." the critic is accusing the speaker of being highly manipulative, filling their talk with so many secret signals that the subtext has become almost impossible for "those in the know" to miss.