There is nothing to be concerned about. If you sign for a letter or package you are acknowledging it was received at the address listed. The person to sign does not have to be the one whose name appears on the package. I've signed for many packages and letters for people at work,
and many others without knowing what was inside. If the package contains drugs, and nothing else, then there is no way to prove it has anything to do with you. It could have been ordered by anyone, anywhere, and simply sent to you by mistake. If it does not contain an invoice, there is nothing to tie you to it. Relax...