Coexist

Picture is courtesy of "marcusg" who published it on Flickr with the collowing caption:

[U2 lead singer] Bono said this was grafitti he saw... calls to peace between the religions, Islam is represented by the cresent moon, star of david for the Jews and Christian cross.

To me it looks like a modern version of the three rhombs idea that is discussed at length in Asher Eder's book THE STAR OF DAVID. 

Bono referred to this symbol as he sang, “Jesus, Jew, Muhammad, it’s true…All sons of Abraham. Father Abraham, speak to your sons. Tell them, No more!”
Bono first saw the “Coexist” symbol painted as grafitti on a wall in Chicago.

Coexist is actually the work of Piotr Mlodozeniec, a Polish graphic designer living in Warsaw. He created the CoeXisT image in 2001 for a contest hosted by The Museum on the Seam for Dialogue, Understanding and Coexistence in Jerusalem. 

Coexist in Amsterdam

Photo of Star of David in the word Coexist on a big billboard poster in a public park in Amsterdam outside the Van Gogh museum is courtesy of
garethmooney from Flickr.

Coexist

Photo is courtesy of Lia Lake.
The slogan coexist includes:

Muslim crescent symbol representing the "C;" the Jewish Star of David, the "X;" and the Christian cross, the "T." ...reminds Christians, Jews and Muslims that we all have a shared heritage, we are all distant cousins – family as well as neighbours. Neighbours who have a lot in common to talk about. Jews and Arabs [who are mostly Muslims] can trace their ancestry back to Abraham and Christians through faith are recognised as his “spiritual” sons.