For those who don't follow the delights of US customs and excise the latest note is that from October 22nd any item of electronic goods (so that'll include locomotives) must have all the valid US approvals (FCC ID etc) or it'll be impounded by their goons.

What does that actually mean?

Stuff shipped to the US, presumably? What is an FCC ID? Does that include second hand stuff, ie are eBay sales implicated?

I did notice upon trying to order something recently that the three shops I've previously used have all stopped shipping internationally (or in one case as good as by making it exorbitant), which I assumed was related to some such nonsense designed to make it harder.

eBay's take on FCC-IDs...

https://www.ebay.com/sellercenter/resources/fcc-id

Applicable if listed on eBay.com or eBay.anythingelse if made available to US located purchasers.

it states "Products that intentionally transmit radio signals like Wi-Fi, Bluetooth, cellular, or other wireless technologies" require an FCC ID. A standard DC loco does not intentionally produce a signal (traditionally many had suppression capacitors built in) but now some Digital systems are moving to wireless technologies those likely do come in to scope...

Surely locos would be exempt, but DCC controllers could well require an FCC ID.

That is only a part of the OP's post though, which suggests there are hoops to jump through for any electronic products.

Any electronic product you ship into the USA must be approved already for the USA and you may be required to provide the approval evidence.

So basically anything electronic now needs an SDoC, a responsible person in the USA and so on. For any product that's sold in the USA anyway that shouldn't be a problem (other than finding all the approval info) for anything not it basically means you can't ship it into the USA full stop unless you get a US responsible person and do US compliance lab testing.

ie if it's a Bachmann loco and Bachmann sell it in the USA already you just need the approval info. If it's a UK designed widget with electronics in it, or a UK motorising kit or similar, have fun.