Symbol recognition is a well-known challenge in the field of graphics recognition. A symbol can be defined as a structure within a document that has a particular meaning in the context of the application. Due to their representational power, graph structures are usually used to represent line drawings images. Thus, a number of graph comparison approaches are required to answer whether a known symbol appears in a document and under which degree of confidence. In this paper we propose two strategies to recognize symbols depending on the type of their substructures. For those symbols that can be defined by a prototype pattern, we propose a graph isomorphism approach. On the other hand, for those structures consisting of repetitive patterns, we propose a syntactic approach based on graph grammars.