How can it be determined whether the deceased was a Muslim or not?

If a deceased person is found and their status is unknown, distinctive signs such as circumcision, clothing, and hair dye are used. If no sign is apparent, then the country in which the person died is considered. If it was in a Muslim country, they are washed and prayed over. If it was in a land of disbelief, they are neither washed nor prayed over, in accordance with the principle that whoever is in a land belongs to its people. This is supported by the hadith (definition) of Al-Sa'b ibn Jaththamah: "They are from among them."