Existing artwork-oriented retrieval-augmented generation (RAG) systems typically support visual understanding through contextual information such as artist metadata and historical background. Symbolic folk-art interpretation instead requires connecting visible motifs to culturally situated meanings. We study semiotic retrieval for this task in Korean minhwa, comparing dense semantic and graph-structured retrieval. We introduce SemioticRAG, which organizes symbolic knowledge through Barthesian Form, Concept, JointConcept, and Myth structures. Blind human evaluation shows that DenseRAG performs best overall, with SemioticRAG ranking second. Qualitative analysis indicates that SemioticRAG produces more explicit pathway-based symbolic compositions, while depending on Form-level grounding and graph construction quality. Overall, explicit semiotic structure changes how culturally grounded meanings are composed rather than uniformly improving interpretive quality.