Here are some photos I've taken while being driven around Cairo on buses or with friends.
Here is a photo I took from the highway of the Citadel, a prime attraction of Cairo, built in 1200 AD as a fortress to protect against the Crusaders. The Citadel has three mosques in it.
I saw one mosque with a crescent moon on top and was told by the person driving me that this was a symbol of Islam. I read online that the origin of the crescent moon with Islam dates back to the Ottoman Empire when a ruler from that empire had a dream about a crescent moon curving over the entire earth. He then adopted the crescent as symbol of his rule. With the Ottoman Empire ruling over the Muslim world in ancient times, the crescent moon became associated with Islam, though the online source I read said many Muslims do not consider it a symbol of Islam since it has nothing to do with Islamic history during the time of Prophet Muhammad.
The color green is often associated with Islam. An Egyptian friend told me that was because green was Prophet Muhammad's favorite color (some say he dressed in green frequently and the banner he went to battle with may have been green); because green represents all living things; and because heaven (or what online seems to be referred to as Paradise) has green everywhere. Here, many of the mosques have strips of neon green lighting framing part of the roof or spire.
On the topic of Paradise, I read one article online explaining what Prophet Muhammad was reported to have said about Paradise. One of the things in the article was that:
"In Paradise there is a tree which the rider of a swift horse would need one hundred years to pass beneath." [Bukharie, Muslim].