address flagging
According to Legal Muscle by Rick Collins, "Customs Special Agent Jameson of the Mail Division was working a detail at Dulles International Airport and came across a suspicious courier parcel addressed to "L. Bates" in maryland. There was no sender's address. he opened it (it was an international package, so he didn't need a warrant) and found "200 dosages of Clenbuterol". The parcel was seized, a warning letter was sent out, and the name and address were entered into the Customs computer database."
That was from page 213.
He also sites several cases where the prosecution used previous instances of international package delivery as evidence. According to Rick Collins, all packages coming from outside the US are recorded in a database. The sender and reciepent name and address are recorded.
Personally, I think that is bullshit, it would take too much time.