It's completely illegal.
Who's gonna do something about it? The FBI?
The problem is they're going to decide who is and is not antifa. If they say you are, then you are. And if they say antifa are terrorists, then they are. Something like this is the end result in the "war on terror" stuff from the early 2000s. Or, alternately, "anything I don't like is woke" except they'll send the cops and/or feds to crack your skull or just straight up kill you.
https://imgflip.com/memegenerator/459874481/Everything-I-dont-like-is-woke
But substitute in "racism".
Doing it for personal use, without profit or gain, is supposedly illegal. Doing it for profit certainly appears to be legal.