Imagine Obama or Elon Musk one day gives this gesture while talking about, say, foreign aid to Africa. Then you know that he's with us, or at least knows about Effective Altruism. There could be a myriad of reasons why he doesn't want to talk about it though, ranging from it being ammunition for Fox News, to perhaps people in his own organization not agreeing with it, and them having to walk a fine line.

Obama uses a secret code for signaling that he's an EA would be ammunition for Fox News. Him speaking positively about the AMF or even speaking positively about GiveWell wouldn't give Fox News good ammunition.