When I created these characters, as I was fleshing out the entire family, I had the idea to give each of them an alliterative name with a double "S" and whichever words that I chose for each one would dictate what kind of personality each one would have and what kind of a silly face each one would have to go along with it. For Slick here, his personality is that of a perpetual prankster, and his face is something of a funny old man look in the stylized yellow smiley face ideal that they all have. His face also matches a bit with his son, Style, since they both have kind of the same big toothy grins. Slick has no shape as a symbol, but rather has his initials inscribed on his huge bow tie, so that is in effect his symbol.