Well by signing something, you are taking ownership for the package and/or acknowledging that you ordered it. In the very rare case of a controlled delivery, this is how "they" bust you.
Just keep your orders small and for personal use. People that get busted are usually receiving larger amounts more often. Or are involved in some other illegal activity, trafficking etc. and are being watched.
So just take a look at yourself, what you do, who you involve yourself with, outside of the IOP/SY world. Most personal users who otherwise stay on the right side of the law should have nothing to worry about. But I do think a little paranoia is healthy to have in this game.