"A Soviet political joke describes a disgruntled man holding up a white piece of paper in the street in protest and, when asked why, the protester replies that everyone knows what the paper is supposed to say."

Its pretty easy to detect the authoritarian states as the ones where people can be arrested for actually doing such.

Happend in China/Hongkong. Happend in Russia. And also happens in the UK.

https://en.wikipedia.org/wiki/Blank_paper_protest