What are Decorated Silver Stake

Rose finds a silver stake in the vault of Galina's mansion that has special designs on the side of it, clearly an important possession of a dhampir. Rose uses this stake to stab Dimitri in the chest, but he falls into the river before she can see if it has penetrated the heart. Later, Rose receives this stake in the mail along with a note from Dimitri promising that he will come after her to kill her.