Regulations are called AAA or "triple A". (Cant remember what it stands for now..its too late at night!)
Its a mandatory requirement by the DoT that ALL baggage is able to be traced to a passenger on board. For unaccompanied baggage (rush bags), an extra certificate is required to prove that extra security screening has taken place for these bags. The flight cannot legally depart without this certificate,
The baggage reconcilation form must be signed PRIOR to push back. This is a breakdown of how many bags are on board the aircraft, unaccompanied baggae, crew baggage and delivery at aircraft baggage.
Aircraft have been called back to stands to investigate possible irregularities.