I’d like to see a statistic for the number of people who believe this sign.
Given that speed limits were initially constructed to save money during wartime (55 mph is the sweet spot on the bell curve of gasoline used per speed graph), the idea that an aircraft (with a much higher carbon footprint than cars traveling 20 miles over) is monitoring speeds on an interstate is not only counterintuitive–it’s absurd.
I guess the chance that people might slow down and save a life is worth the cost of a couple signs.