No, it's against "the law." It's hardly a crime.
But semantic distinctions aside, I really don't care if it's a crime or not. If the US governments fucks with me and pisses me off, I'm going to do what I'm going to do.
It’s far better to work to make such activities illegal than to do your complaining from behind bars.
That's not really an either/or thing. They haven't (yet, as far as I know) put one of these on my car, and I work on making things like this illegal though the political process . And I'll continue to do so, up until the (hypothetical) day that I wind up behind bars for fucking with one of their silly little tracking devices.
All that said, I can't imagine them ever getting a conviction in a jury trial, on a charge of "tampering with a government owned device" if it's not labeled or anything. It's totally reasonable to say "Oh, I found this thing on my car and I didn't know what it was so I took it off and threw it away" or "I knew what it was, but I assumed my crazy stalker ex-girlfriend put it there," etc. Getting any reasonable jury to convict on this would be insanely difficult.