[nuker]

You get a prompt to enter Bitlocker recovery key if you turn off Secure boot in BIOS.

[AnthonyMouse]

That's Windows doing that, which they've just compromised and then configured to display only the normal login prompt but send your credentials to the attacker.

They can also decrypt your hard drive by doing the same thing without modifying the original machine by just stealing it and leaving you a compromised one of the same model to also steal your password.

[nuker]

If evil maid attack, and you see this prompt, you a) re-enable secure boot, if did not work b) throw away the device.

In any case data stays secure.

Edit: Hmm, you have a point, how do I know secure boot was disabled in the first place? Anyway, still works for servers and unattended reboots.