The Way I see it

"Policemen and security guards wear hats with a peak that comes down low over their eyes for psychological reasons. Apparently eyebrows are very expressive and by covering them up you appear a lot more authoritative. The upside is this means it's harder for cops to see anything more than six foot off the ground and maks painting rooftops and bridges a lot easier."

- Banksy in Banksy: Wall and Piece p.42