They have computers also. Another way of doing this is to take pictures of the items you have marked. On the back of the photo you can mark the serial number and model number of that particular item. If you have a video camera, you can use that also. Describe the item your filming with it's serial number and model number.
Jewelry is hard to mark, so keep all the heirlooms in a safe.
There is a lot of cases where the thief was caught in another state, and the merchandise was never returned to the rightful owner because the police could not identify it. You could have your house boarded up like Fort Knox, but if someone wants to get in they will find a way. People that have alarm systems feel that they are safeguarded against everything. There was a case in my own neighborhood were a house had a security system installed, and the burglar cut the phone line. Well, a lot of good that system did without a call out.