Is federal obscenity law enforced? I doubt it can be enforced either, with the decision in Reno v. ACLU that struck down similar provisions of the Communications Decency Act as violating the First Amendment.

> If it's illegal to posses something, the government can ban offering to sell and distribute it.

This is begging the question, because first you would have to show that banning the mere possession of adversarial images doesn't violate the First Amendment. Otherwise you can make it illegal to possess books in a way to prevent the sale and distribution of literature.

> Is federal obscenity law enforced?

It seems to vary. Typically not, and when attempts are made court verdicts seem to be mixed. But unfortunately sometimes people do get convicted and the convictions upheld. For example, United States v. Whorley. https://caselaw.findlaw.com/us-4th-circuit/1431669.html

To be fair, obscenity laws don't seem (to me) to be in keeping with the rest of the laws surrounding freedom of speech in the US. They are shockingly vague and have been used to prosecute people for artwork (!!!) in the past. Court verdicts for such laws seem to be mixed - sometimes they go along with them, sometimes they side with freedom of expression.

> offers to engage in illegal transactions

Just to clarify, that means "offers to engage in crime". Other than the aforementioned obscenity laws freedom of expression is generally quite well protected in the US so there won't be a crime in the first place (and thus related transactions won't be illegal).

> If it's illegal to posses something, the government can ban offering to sell and distribute it.

I think you misunderstand slightly. If it's illegal to possess something then it is _already_ (to the best of my knowledge) illegal to offer to sell or distribute it. The question is what the government is and isn't allowed to ban possession of.

Interestingly, in the case of "obscene" materials possession itself isn't banned. Only import, sale, and distribution.

The issue with "People who create and distribute these stickers knowing their purpose should go to prison." is that such a wording seemingly bans them outright regardless of intent. That is an affront to freedom of expression. If I want to craft adversarial examples I shouldn't need to justify my intentions and seek permission up front. An action should need to be justified as illegal on a case by case basis, not the other way around.

Note that it is already illegal to deface street signs so by extension if you create and distribute stickers with the express intention that they be used that way then presumably you are already violating the law today. On the other hand, such stickers are not (currently or ever, I hope) inherently illegal in and of themselves.

I'm not misunderstanding, although I agree that all this is largely beside the point.

It's not obviously true that the illegality of possession automatically implies the illegality of the offer to sell. Consider for example a case where the seller doesn't actually possess the item, but merely offers to sell it. In this case, the supreme court upheld a law making such offers illegal. Without the ruling, you might argue that the mere offer is protected speech.

The point of all this is really indirect though. I'm just saying that in cases where "speech" concerns illegal items, like nuclear weapons, child pornography, and drugs, sometimes the government is given more leeway in controlling speech related to items.

Is there a law against teaching someone how to make nuclear weapons? There are certainly export controls, and almost anyone with the knowledge is subject to NDAs with the government, but are there any actual laws criminalising telling people how to make nuclear weapons?