Theives breaking into vehicles for GPS navigation device

Many realtors use GPS Navigation devices when traveling to show homes with their clients. It is now coming to our attention that this wonderderful tool is ending up in the hands of theives. We are now being instructed to take the GPS device out of our vechicles when we leave our vechicles, and to also take out the mounting brackets that hold these electronic devices. How nice it would be if our fellow Realtors double checked the directions written for their listings, making sure none of us would get lost.