[wongarsu]

Are you even legally signing anything if they can't show you the document you are signing?

I am not familiar with the nitty gritty of US law, but under German law that signature would be worthless. Even signing a document you have but are unwilling to read is legally a bit iffy (which is why for things like real estate a notary will read the paperwork to you and ask if you understood it, or why surprising clauses in terms of service are unenforceable). Signing something without being able to know what you are signing would be worth exactly nothing, because you didn't actually knowingly consent to any particular thing, and neither did you have the "meeting of minds" required to form a contract.

[Telaneo]

It probably would be unenforceable in the US too, given you have no opportunity to know what you're signing, but you'd probably have to drag it before a court to settle that, and US companies know that no* individual is actually going to do that over what ultimately is (likely to only be) a minor inconvenience.

* Within margin of error