So basically we have (a joker) using sadness to create smiles. I doubt Oda named both objects that way accidentally. So does anybody know if Oda has ever mentioned what the symbolism is behind S.A.D and Smiles?
SAD and SMILES are named after the side effects of Artificial devil fruits
A normal devil fruit grants power and has only a side effect of unable to swim, but artificial devil fruits are different on top of unable to swim
they also lose the ability to become SAD or angry, they can only SMILE or laugh
Source: Chapter 943: SMILE