If you mark your property, you increase the risk a criminal must take when he steals your valuables, and you have a better chance of having your property returned to you. Further, property marked has a reduced resale value to the thief making the property less attractive.
Marked property is easier to identify.
Sometimes when stolen property is located it is your word against the thief, but if the property is marked with your identification you can easily prove it is yours. The police also use the identification markings to trace property back to the thief even after he has disposed of your property. Part of Operation Identification is maintaining a property list. Not only will this help you inventory your missing valuables in case of theft, it will also make an insurance inventory much easier and less subject to being contested in cases of fire or wind and storm damage. List all household and personal effects and their serial number if applicable, and please remember to keep the list up to date.