A smile is an abstract expression, is it?

This is what emoticons would look like if they were designed by famous artists. Who would have designed the one on the bottom left?

Apologies for the inordinate delay in updating the post. Answered correctly by mg, Anon, mit, t@β!я я@kђ$ђ!ηd@ ђů$$é!η, Arnav, and M.o.P.

Source: The History of Art
Answer: Mark Rothko