It makes sense that symbology is the study of symbolism, and that symbolism is the practice of representing things with symbols. But are these two words also used as synonyms? One definition for symbology, for example, is the "use of symbols," which seems to me identical to the definition of symbolism. I came across symbology in this movie critique, and I would have used symbolism:

"There is some symbology in the movie, involving a construction site and Kelli's interest in ecology, but the movie is not really interested in saving the environment, it's interested in characters who say they are interested in the environment because, after all, who isn't, or shouldn't be?"

[Some sentence, right? Four times he used the word interest or interested.]