While an Orthodox tradition is to use no greetings on Tisha B’Av, I believe changing this very negative absence of greeting to —instead—a world-improving blessing as a greeting on this day, could be an opportunity for Tikkun Olam as it would place millions of blessings into the world on Tisha B’Av to help bring it improvement. My suggestion is that this new greeting on Tisha B’Av will be Shalom B’Olam or Shalom BaOlam, to help bring peace everywhere in the world, on this day that represents so sadly and clearly what can happen in the world without Shalom BaOlam.
I would love to know what people think about this suggestion and how best to make it happen.