All it does is flash (shut them off as long as you hold it down) the headlights to let the person that just passed you know it's OK to come back over. If you have another similar button on the right side of the wheel it'll blink just your taillights to "thank" the guy that just said OK using their ICC button. It's the trucker code of polite and helpful. Use them.
It stands for Interstate Commerce Commission, the trucking regulators...
2007 and 7/8ths Newmar Essex 4502