"Yeah, when I'm done with a USB stick I wipe it with random noise, so that I know that the data I'm finished with is properly deleted."

Usually when you encrypt a drive there's a telltale header, so the disks wouldn't be "seemingly encrypted" at all — and wiping disks clean with noise isn't especially uncommon. It's as plausibly-deniable as it gets, and it'd certainly fly in court.

>Usually when you encrypt a drive there's a telltale header

Not necessarily.

https://www.truecrypt71a.com/documentation/plausible-deniabi...

2. Until decrypted, a TrueCrypt partition/device appears to consist of nothing more than random data (it does not contain any kind of “signature”).

Huh — I was unaware that TrueCrypt has plausible deniability by default. I know it's possible to set up plausible deniability, but with LUKS that takes extra steps, and I assumed the same was true of other disk encryption schemes.