What does the dashboard light with an orange triangle exclamation point inside on a Mercedes mean?

Low Coolant Level. Your coolant level is low, and you must check your coolant ASAP when it is safe to do so. Failure to keep the coolant topped off and allowing this light to stay on for too long might result in severe engine damage due to overheating. Low antifreeze or coolant levels pose additional issues in colder driving circumstances because the coolant also functions as your engine block's antifreeze.