[waste_monk]

> Hypothetically it would be legal to display that in public in the US

Would it? I'm certainly not a lawyer or ITAR expert, but I would think that if you walked through a public space where you couldn't positively confirm that everyone present (and everyone who might view it transitively via video recordings, live streams, etc.) was OK to access the materiel on the shirt, that would be considered an export and you'd be in big trouble.

[mothballed]

I'm no ITAR expert either, but IDK how wearing a T-shirt could possibly be an export. My lay understanding of export is that the information would somehow have to leave the country; if someone looks at the T-shirt and transmits it out the country they'd be the exporter, not the person wearing the T-shirt. If someone records the t-shirt and transmits it, they'd be the exporter.

[waste_monk]

>My lay understanding of export is that the information would somehow have to leave the country;

It's not just physical items like munitions, but also things like transfers of information (blueprints, technical data, documentation, etc.) or services being performed, regardless of where (inside or outside the USA) or how (paper, electronic, verbal, etc.) it takes place.

Have a look at [1] § 120.50 (Export) and § 120.63 (definition of Foreign person).

>if someone looks at the T-shirt and transmits it out the country they'd be the exporter, not the person wearing the T-shirt.

I believe the person wearing the shirt would be considered the exporter, as that is the point where the information moves from (I'm assuming for the purposes of conversation) an USA citizen to a foreign person.

But again, I could be wrong. Safest bet is not to print the shirt to begin with :)

[1] https://www.ecfr.gov/current/title-22/chapter-I/subchapter-M...

[mothballed]

Hmm... I'd be interested to look at any 1A cases regarding that. I'm unable to find any 1A exceptions regarding mere information on weapons. The US is allowed to suspend constitutional rights at border controls, which is how they prevent exporting the information outside the US, but I'd bet dollars to donuts the blueprints/information part is unenforceable as non-commercial speech within the US.

Here's an example of T-shirt with a machinegun blueprint on it for instance, for sale in USA without any checks as to your immigration status [note US law considers a device that induces automatic fire as a 'machinegun' despite the fact the device itself isn't really a gun]:

https://ctrlpew.com/product/yankee-boogle-tee-gatalog-editio...

[dlgeek]

I'll continue in the "not an expert" chain, but my understanding is that ITAR's prohibitions include communicating the information to a non-US person (a US person is a citizen or permanent resident), even if that is done on US soil.