Three Seals == 三法印（诸行无常，诸法无我，寂静涅槃）
Also known as Three Universal Truths.
1.All phenomena are impermanent.
2.All Dharma are not-self.
3.The eternity is Nirvana.
It is called the seal because it is to certify whether it is the Buddha's teaching or not. Also see Four Seals.