I have been reading so many comments saying, "don't sign for it" or "just no matter what you do, don't sign for it". I am tired of reading this, and I believe some of this is coming from people's fascination with crime shows. A signature is not going to inherently condemn you. More often than not, it's your record as far as the system is concerned. It will also be based on an intensive investigation. Also, if they catch small amounts it's simply easier to throw it away than go through a legal battle for $100 worth of drugs.
Lots of international mail service providers require a signature for tracked packages.
Spreading this in comments creates a false sense of security and therefore weakens security. Always have a fire under your ass as far as security goes.
I think it's bc people wish a loophole existed that could guarantee to keep them outta trouble. Signing won't convict you nor will not signing guarantee you get a free pass.