Of course this isn't the only crime prevention step you should take if you are away. Taking care of the mail, and arranging for proper lighting both help keep a burglar in the dark. In crime prevention, as in many other parts of life, little things can mean a lot. Take, for example, a car's cigarette lighter. It may not look like much to you, but it can send an important signal to thieves.
Some criminals look at the dashboards of cars.
If they see the cigarette lighter is missing, they figure there is at least a possibility that it has been taken out to accommodate a battery charger or power adapter for a cell phone. They're willing to take a chance that the cell phone is not far away - maybe stored in the glove box. So, when they don't see a cigarette lighter in a car, some thieves will break the passenger side window, and open the glove box, hoping to find a cell phone inside. If you don't have a cell phone, the criminal will just move on, looking for another opportunity. Don't give criminals an opportunity.