When you see a buoy with number 4 and flashing light what should you do?

A buoy with the number 4 and a flashing light typically indicates a navigational marker, often used to signify a channel or hazard. You should maintain a safe distance from the buoy, keeping it on your starboard (right) side if you are traveling upstream or toward the port (left) side if going downstream, depending on local navigation rules. Always consult the relevant nautical charts and guidelines for the specific area to ensure safe navigation.