You can only reasonably do this is the police use your bootloader. The destroy code would need to have the exact same wording ("Unlocking device" or whatever) and while actually writing random data over the disk and leaving you with "Unable to open volume."
Now if the police had made a copy, they could tell between the two copies that one version zeroed the disk.
In reality, the police would remove your disk and not use your bootloader. You would need to use an encrypted format that actually ran some application code as the result of a specific key, with that application code itself encrypted by said key. It would have to be integrated as part of the unlock process. LUKS doesn't provide any of these mechanisms by default.