The smiley is an example of a visual meme. Once seen, you are likely to copy it, reproduce it and show it to others.
A meme (rhymes with "dream") is a unit of information that replicates from brains or retention systems, such as books, to other brains or retention systems. In more specific terms, a meme is a self-propagating unit of cultural evolution, analogous to the gene (the unit of genetics).