John and Linda,
The battery parallel switch or boost switch that ties your house and coach batteries together should have a picture of a battery on it. The switch that you described with a zigzag pattern on it is the switch that turns on the heater in your outside mirror. Like you said, hopefully you will never have ice or snow on your outside mirrors where you need heated mirrors, or a dead battery where you need the boost switch, but you should know that they are there if you do need them.
Gerald