Many people in the United States believe in the separation of church and state. That's reflected in our flag, which has only secular symbols on it. But many other countries have flags with religious symbols on them. Indeed, according to the Pew Research Center, nearly a third of the 196 countries in the world, have flags with a religious element.
Almost half (48 percent) of the 64 flags in this category contain Christian symbols — usually a cross. A third (33 percent) contain Islamic symbols — typically a star and crescent. Christianity and Islam are the world's two leading religions.
Buddhism and Hinduism are represented on five flags, according to Pew. There are also flags bearing symbols representative of Incan, Aztec, and Shinto spirituality. Israel is the only country with Jewish symbols on its flag: both the Star of David and a tallit or Jewish prayer shawl.
The US flag does not contain religious symbols, but, as Pew notes, several US state flags do, including New Mexico, Alabama, and Florida.
Update: This article has been updated to show that several US state flags contain religious symbols.