I'm reading Mindf*ck at the moment, the book by the Cambridge Analytica whistleblower, and it's pretty eye opening.

Basically using big data to identify a small number of people you can manipulate to change the outcome of elections. Billboard data surely feeds into that, if you can identify individuals from it (which you might not be able to today, but as you say, getting people comfortable with surveillance will allow more invasive iterations of the technology).