This is a hard one to answer. The reason is that you are asked to distinguish between 2 schools of thought that are very close together. Not only that, but the characteristic you are looking for is not mentioned in either description.
Since semiotics brings in many more fields of study than does iconography, then I would go with iconography. This school of thought seems content just to find the symbols according to its description. What is done with them is mentioned in the other school but is not elaborated upon.
