As the label suggests, predicative adjectives function as predicates, hence are used to state something about the noun. Contrary to their attributive counterpart, predicative adjectives are not included in the noun phrase. An illustrative example is reported below.
re
furniturea ix(B)a old
‘The furniture is old.’ (adapted from Bertone, 2011: 8)
The predicative nature of the adjective old can be recognised through the following cues: i) absence of the non-manuals characterizing noun phrases, ii) presence of an (optional) localising pointing sign between noun and adjective, and iii) a prosodic break combined with a head nod signalling the boundary between noun phrase and verb phrase.
The pointing sign ix can be expressed by the dominant hand after the noun or, alternatively, it can be expressed by the non-dominant hand while the dominant hand articulates the noun furniture.
Some predicative adjectives might allow for aspectual inflection. This is discussed in MORPHOLOGY 3.3. Syntactic characteristics of non-verbal predication are addressed in SYNTAX 2.1.4.