Visual Language, a term introduced by Robert Horn, refers to "language based on tight integration of words and visual elements". The visual elements include shapes, as well as images (e.g., icons, clip art).
What does this have to do with memory? Well, partly of course, because the appropriate use of images usually makes information more memorable, but visual language has considerably more to offer than that. To appreciate what it is, Horn has examples at http://web.stanford.edu/~rhorn/