I'm trying to "hardware-lock" some software written for the Pi and ensure that even if someone clones the SD card, they're unable to run a particular piece of code if it's not on an "acceptable" Pi. To make a Pi acceptable, I'm thinking of writing a value to a register somewhere on the Pi, and have the software read that value before it starts. If the particular register reads what it should, then the software will run. It doesn't matter which register, nor what the value is - could even be as simple as whether a bit is HIGH or LOW.
Is there a register I can write to that will maintain that state even through power cycling? (Or is there another, better way to do this that I'm completely overlooking?)