This paper illustrates developments of signatures for Artificial Intelligence (AI) applications. Since the signatures are data structures with efficient results in modeling of fuzzy inference systems and of uncertain expert systems, the paper starts with the analysis of the data structures used in AI applications from the knowledge representation and manipulation point of view. An overview on the signatures, on the operators on signatures and on classes of signatures is next given. Using the proto fuzzy inference system, these operators are applied in a new application of fuzzy inference system modeled by means of signatures and of classes of signatures.