The problem is, when you have to explain it, it probably won't be the best, and trying to come up with a good thing for "external expressions" will be tough. People think of external expressions in different ways. Like for me, the way I keep my apartment tidy is an external expression of myself due to my OCD, but other people who don't know me won't understand. Where as, a facial expression isn't really considered an external expression. If you did a super basic silhouette or something, like the idea of the thinking man statue, and try to add the full name "external expression" so that people can relate the text to the symbol, you will get a better one.