I dont think that this gesture of Kohli required any kind of penalty BUT current code of conduct states that he should be punished.
BTW, Personally I am for scrapping all such foolish ICC code of conduct. Unless its something really serious such as Ponting doing animated argument with Aleem Dar and almost refusing to accept 3rd Umpire’s decision having said that, I am sure you will agree that at times BCCI was able to twist arm of ICC due to its financial strength.