It's not for underhanded secret deals. It's to allow you to know who you can trust with information such as "I am an effective altruist and may be a useful ally who you can talk to about stuff".

Ideally one might want to overtly talk about effective altruism, but what if circumstances prohibit it. 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.

We can drop the hands behind back part and make it as subtle as you want. I'm not beholden to the specifics of the gesture, so much as just offering the merits of the idea itself.

Maybe it's a bad idea that would hurt us more than help us. In which case, it's good to get the debate out of the way quickly, and I appreciate your response.