the '3 characteristics of existence', or signata, are impermanency (anicca), suffering or misery (dukkha; s. sacca, dukkhatā), not-self (anattā).
"Whether Perfect Ones appear in the world, or whether Perfect Ones do not appear in the world, it still remains a firm condition, an immutable fact and fixed law: that all formations are impermanent, that all formations are subject to suffering, that everything is without a self'' (A. III, 134).
"What do you think, o monks: Is corporeality (rūpa) permanent or impermanent? - Impermanent, o Venerable One. - Are feeling (vedanā), perception (saññā), mental formations (sankhāra) and consciousness (viññāna), permanent or impermanent? - Impermanent, o Venerable One.
"But that which is impermanent, is it something pleasant or painful? - It is painful, o Venerable One.
"But, of what is impermanent, painful and subject to change, could it be rightly said, 'This belongs to me, this am I, this is my ego'? - No, Venerable One.
"Therefore, whatever there is of corporeality, feeling, perception, mental formations and consciousness, whether past, present or future, one's own or external, gross or subtle, lofty or low, far or near, of all these things one should understand, according to reality and true wisdom: 'This does not belong to me, this am I not, this is not my ego' " (S. XXII, 59).
"In one who understands eye, ear, nose, tongue, body and all the remaining formations as impermanent, painful and not-self, in him the fetters (samyojana, q.v.) are dissolved" (S. XXXV, 53).
It is the full comprehension of the 3 characteristics by direct meditative experience which constitutes liberating insight. About their relation to the three gateways ot liberation', s. vimokkha I .
For further details, s. anicca, dukkha, anattā, vipassanā.