Chomsky (2013; 2015) assumes that syntactic objects (SO) must be labeled for interpretation at the interfaces, proposing the labeling algorithm (LA), which deals with three types of SO. One of the three types, an SO of the form [XP(P) YP], where XP and YP share the most prominent feature F, receives F as the label, according to the Labeling Algorithm (LA). While this proposal applies to "asymmetrical" XP-YP structures, in which the interpretable F on XP and the uninterpretable F on YP match and agree, it is not clear if the proposal also applies to "symmetrical" XP-YP structures such as [NP) NP], where the features shared by the two terms are both interpretable. In this theoretical context, I present two instances of structures of type [NP(6) NP1] - symmetrical NP-NP structures found in Japanese Sign Language: identity copular sentences and NP-coordination. It is shown that in both types of constructions, symmetrical NP-NP structures result in ungrammaticality. I next propose an account of the unavailability of symmetrical NP-NP structures in JSL in terms of a failure of labeling. Finally, I discuss a possible consequence of this proposal for simultaneity in sign languages.