It is an absurd and fucked up situation, but they tend to use your signature as proof that you accepted the package. I have heard of cases where they don't try to get a signature during a CD and use other techniques, but very frequently they wait for you to sign before they arrest you. It at least seems like they use the signature as proof that you ordered the package. I have also heard of them pretending to be a neighbor who was delivered the package by mistake, and then asking you if it is yours and arresting you after you accept it. Of course if anyone has a neighbor ask them if this mail addressed to them is theirs, they will probably say "yes" also....