Your logic is perfectly fine but the problem is you are assuming that LE use logic. Or that the jury will use logic. Or that it will ever make it to a jury. In reality signing for the package means you accept ownership of the package, and even though it might be possible to argue against this in court, in practice they usually try to get you to sign for it (even if it is sent in a way that doesn't require signature). If signing for it wasn't bad for you, they wouldn't bother trying to get your signature.