The arrangement of five units in the patter corresponding to the five-spot on dice, playing cards, or dominoes. A quincunx is often used in Hoodoo as a sort of "artifical crossroad" and can be created inside a room in the house. The quincunx or five-spot is generally used for scaling and fixing spells in place.
Sam: You see this pattern here? (tapping a five-point symbol engraved in the urn) That's a quincunx, that's a five-spot.
While investigating Sam finds an urn in the hallway with an inscribed quincunx and Dean sees a photograph of a Rose and her nanny, who is wearing a quincunx necklace.