In some Buddhist traditions what distinguishes a Buddhist from a person who is not a Buddhist are what is called The Four Dharma Seals.
The first seal states that all composed things (sarva-samskrita) are impermanent (anitya). The second seal states that everything that deteriorates is suffering (sarvs??srava-dhhkha), for example, the Five Aggregates consisting of form, sensation, perception, habitual tendencies, and sensory consciousness. In fact, these aggregates, i.e., the psychophysical organism, are synonymous with suffering or duhkha. The third seal states that nirvana is peace or sh??nti. The fourth seal states that all things are empty (shunya) and not of the self or ??tmaka.