@sandofsky I used to design and make signs just like these.
YES, I specified polarisation angle.
NO, the purchasing people did not think that was important, and chose 'cheap' as the primary factor.
Hence the effect.
In later life I've come to hate the works of my younger self, and like you, I ADORE the fact that sunglasses block them.
Question for the crowd. Why aren't car headlights horizontally polarised for the same effect?