Those with even a rudimentary grasp of national issues know that the free speech guaranteed by the first amendment to the Constitution and the Bill of Rights isn't limited to personal verbalization. The concept has morphed into "freedom of expression", which might include art works. Nude dancing, flag burning and campaign contributions as well as pornography have been considered as examples of free expression.
Non-verbal expression can and does include activity that is somewhat less apparent at first glance. The pledge of allegiance, at one time a staple primary school morning ritual, has fallen into disuse. An adult American rarely recites these words, even in a public setting, probably never to himself. Yet, there is a pledge of allegiance that millions of Americans voicelessly utter each day. They buckle their seatbelts. By doing so, drivers not only buy in to the theory that government knows best, they demonstrate that they're a legitimate part of the program, that they're giving the state's coercion a thumbs-up. Certainly many drivers give this endorsement reluctantly, but that doesn't matter to the state. They have agents that can make your life miserable if you care to exercise what you mistakenly believe to be your freedom. If you simply forget to click, they're on the look-out for that, too. Carelessness is to be punished just like defiance.
The state may not be able to read your mind (yet) or mandate your clothing but they can require you to display an easily seen and enforceable expression of subservience. Always buckle your seat belt.