Ok just a random thought, what about a user could download the seedsigner binary, verify it like normal but than sign the binary using his Nostr or even bitcoin key and part of the signing process is applying a PIN code to the binary. Now he flashes the binary and every time the seedsigner boots he needs to enter his pin or scan a login QR code as a challenge, if correct the ui would show something that only the owner knows if not you know it’s tempered.
Discussion
Tampered.. heck could even be a standard two factor code that you insert on signing the binary that works with standard OTP Authenticators
Can't do TOTP if the device doesn't know what time it is! There's no Raspi Zero clock battery so it's the beginning of time every time you power it up.
So another idea could be preparing multiple cheap SD cards and each one is hidden in a 3D printed seal that nobody knows contains the SD card. If you don’t use it for longer period you move on to the next sealed SD card.
That would probably introduce enough complications to make an attack improbable, but I think someone could still get around it.
They could basically run your protected version through a secret internal emulator, pass the PIN you enter off to the emulator, and play back what the emulator produces.
This all being said, in most cases these exotic, sophisticated attacks wouldn't even happen; it'd just be a $5 wrench attack if they have physical access into your home.
I was told inflation killed the $5 wrench