Ānimitta

ānimitta (P. animitta; T. mtshan ma med pa; C. wuxiang 無相) is translated as "signlessness," "absence of characteristics," "absence of attributes," "absence of defining characteristics," "without signs," etc.

Signlessness (ānimitta) is one of the three gateways to liberation; the other two being emptiness (sunyata) and wishlessness (apraṇihita).

Generally understood, "the recognition of signlessness, or of the absence of characteristics, means that there is no conceptual identification of perceptions."

The Princeton Dictionary of Buddhism states:

A sign or characteristic (nimitta) refers to the generic appearance of an object, in distinction to its secondary characteristics or anuvyañjana. Advertence toward the generic sign and secondary characteristics of an object produces a recognition or perception (saṃjñā) of that object, which may in turn lead to clinging or rejection and ultimately suffering. Hence, signlessness is crucial in the process of sensory restraint (indriyasaṃvara), a process in which one does not actively react to the generic signs of an object (i.e., treating it in terms of the effect it has on oneself), but instead seeks to halt the perceptual process at the level of simple recognition. By not seizing on these signs, perception is maintained at a pure level prior to an object’s conceptualization and the resulting proliferation of concepts (prapañca) throughout the full range of sensory experience.

The 84000 glossary states:

In ultimate reality, there is no sign, as a sign signals or signifies something to someone and hence is inextricably involved with the relative world. We are so conditioned by signs that they seem to speak to us as if they had a voice of their own. The letter “A” seems to pronounce itself to us as we see it, and the stop-sign fairly shouts at us. However, the configuration of two slanted lines with a crossbar has in itself nothing whatsoever to do with the phenomenon made with the mouth and throat in the open position, when expulsion of breath makes the vocal cords resonate “ah.” By extending such analysis to all signs, we may get an inkling of what is meant by “signlessness,” which is essentially equivalent to voidness, and to “wishlessness”... Voidness, signlessness, and wishlessness form the “Three Doors of Liberation.”

Sources

• Buswell, Robert E.; Lopez, Donald S. (2014), The Princeton Dictionary of Buddhism, Princeton University 
• མཚན་མ་མེད་པ་, Christian-Steinert Dictionary
• Three doors to liberation, Samye Institute