Refering to police officers po-po,pigs,five-o ect. The old style six shot police .357 magnum or the like in a holster, hence the bullets are six in quanity and facing down.
Down like six thirty - A phrase popularized in urban hip hop as a term for extreme agreement or participation. It was derived from a visual reference of the face of an analogue clock commonly worn around the neck as part of early hip hop fashion. At 6:30 both hands of the clock point downwards. The phrase is usually accompanied with an exaggerated motion of the speaker thrusting both hands downward to further exaggerate the exclamation.