Four Dharma Seals are the four characteristics which reflect true Buddhist teaching . It is said that if a teaching contains the Four Dharma Seals then it can be considered Buddha Dharma. although the Dharma Seals were all introduced after Gautama Buddha died.
The Four Seals
The Four Seals are as follows:
As suffering is not an inherent aspect of existence sometimes the second seal is omitted to make Three Dharma Seals.
References
Four Dharma Seals Wikipedia(Text) CC BY-SA