It's political speech. Always has been, although there were times when there was less (or no) tolerance for doing so.
IMHO one of the few benefits of the flag-burning cases of the 1960s-70s was that folks were forced to decide just where they stood on the whole "freedom of speech" issue. It often takes more courage to stand up and say "I may disagree with what you say, but will defend to the death your right to say it" than it does to expound on some jingoistic dogma about what the flag does or does not represent.
I'd venture that 99.9% of Americans have no idea what it is like to live in a system where what you say is highly monitored and highly controlled. From personal experience I can tell you that it is a tremendous shock to find out that being an American citizen does not count for squat in certain situations. Being young, and being willing to leave that very day, were the things that probably got me out of the police station without making a lengthy stop at the prison. That, more than anything, made me realize what "freedom of speech" means.
stay safe.