The Arab Spring in Egypt is resulting in riots and persecution targeting Coptic Christians, who make up some 10% of the population. This weekend some 17 were killed. See this.
So how can Egyptians tell if one of their countrymen is a Christian? Well, in an act of defiance and self-identity and so everyone will know their religion, the Copts wear their faith on their sleeve, as it were. They tattoo a Coptic Cross on their wrists. (We blogged about this before, but I found a picture.)